Unggoy

"Leader dead, run away!!"

- A frightened Unggoy Minor witnessing its leader being killed.

The Unggoy (Latin, Monachus frigus, meaning "cold monk") are a small species of servant warriors in the unified races of the Covenant. They are the lowest rank and are usually just used as cannon-fodder. They are classified as a Therapsid, or a warm-blooded reptile, like those of the late Permian period of Earth's geologic history.

Description
They have grayish-blue, scaly skin and small black, bead-like eyes, although some have reddish-orange eyes. Humans have termed such warriors Grunts, due to their size, and because of their speech patterns Furthermore, they are typically poor and cowardly warriors, are physically diminutive, wear minimal armor, making them very vulnerable to ballistic weaponry, plus most of them are tactically inept. However, what they lack in ability they make up for with sheer numbers, as they breed in large numbers relatively quickly and are actually quite accurate with their Plasma Pistols. In some cases, a squad of Grunts has been known to overpower careless marines and the conflict on Harvest was started by an Unggoy named Yull tearing apart Private Osmo. Spec Ops Grunts are far more tenacious than the lower tiered ones, and have even been known to carry Fuel Rod Guns and wear black armor, which makes them extremely dangerous foes.

They are unusual in the way that they breathe methane rather than oxygen. Their combat armor/harness has an integrated methane re-breather system, as Grunts appear to be unable to survive long without methane due to asphyxiation much like humans without oxygen, yet in Halo 3, knocking the methane tank off of them will still cause them to linger around for a long period of time. It may be a hindrance to the Unggoy's natural ability.

They act very stupidly and cowardly when in danger. They are the comic relief through most of the Halo series, as quite often they will say something completely unexpected, and are liked by most Halo fans much more than any other Covenant species. With the IWHBYD Skull activated, the sleeping ones can sometimes say, "Merry Christmas".

There are many groups of Grunt fans, which often come in small Bungie.net Fan-Clubs, and most likely think of Grunts this way because of "sympathy" due to the Grunts' role as the "weakling" in the Halo series, or seeing their value as the comic relief role in the game.

Culture
Grunts were the second race to be integrated into the Covenant (not including Prophets and Elites) (about 402 years) before the events of Halo 3, roughly coming to their indoctrination in 2142 on the Military Calendar. Before joining the Covenant, the Unggoy had attained Tier 4 technology on the Forerunner charts. While not overly intelligent or creative, they are one of the most cordial and sociable of the Covenant races as they possess a very strong pack mentality, often associating with each other in groups, instigating them to present danger when encountered in large numbers. The Grunt pack mentality can be compared to the Brute pack mentality but less violent. Examples are that Grunts and Brutes often travel in groups. Also, Grunts care for fallen pack members, as do Brutes.

Grunts are found seemingly everywhere in the Covenant. They are mostly used for general labor and to serve the higher Covenant, like Elites, although their most prominent role is as the backbone of the Covenant military's ground forces. While individually they are poor soldiers, they make up for this with massive numbers. Due to the amount of Unggoy in the Covenant, they are typically deployed as disposable cannon fodder. Indeed, they have been known to be sent into live mine fields to simply clear the way for the rest of the force, and to be thrown relentlessly at a heavily defended position to overwhelm an enemy force with their sheer numbers. Overpopulation is a serious problem and in non-war times strict laws are placed on Unngoy breeding.

Grunts are essentially a slave race, which obey the other Covenant races out of fear, not will, because they have no political power in Covenant society and the highest political rank available to an Unggoy is a Deacon. However, within the Grunt community there is a strong hatred of other species, especially Jackals. It has been indicated that at some-time in the Covenant's history, in the Eighth age - The Age of Doubt - there was a Grunt Rebellion, which was quelled, thanks in part to an Arbiter who was called upon during that period for that purpose. This fear also leads to a lack of political loyalty during the Covenant Civil War, the Grunts did not ally with a particular side and stayed with whoever commanding them, most likely out of subservient fear to their masters and inability to leave to join the Elites however, many held support for the Elites and still revered The Arbiter.

Due to their low status, Grunts are not permitted by the Elites to possess family names; their names instead consist of one or two syllables, usually with a repeating group of letters. They do value their ties to their offspring, but are usually separated from their families at an early age, by the requirements of their military service to the Covenant. The Grunts resent this greatly, but due to their social status in the Covenant are unable to muster any response. It is also interesting to note that Grunts do appreciate many of the luxuries presented to them in their service to the Covenant, one of them being heat, as stated by the Grunt, Kwassass.



Grunts generally follow a few short, simple guidelines given to them by the Elites; namely "When in doubt, shoot" or "Stay out of the way, live another day."

Grunts feel secure when in large numbers or led by an Elite or in the case of Halo 3, a Brute, though if the Elite or most of the squad dies, or if a superior enemy gets too close, they tend to panic and flee. This causes them to be extremely vulnerable as they are rather sluggish and weak, but given the time or when boxed in a corner, they will turn around and once again attempt to fight back against the enemy. Higher-ranking Grunts typically have superior morale and are less likely to panic and flee in combat. It should be noted that Heretic Grunts, unlike their mainstream brethren, will not flee in combat if the enemy approaches, but will cower in the presence of the Flood. It is unknown why Heretic Grunts have better morale than other Grunts. One possible explanation could be that their enemy is the Arbiter, and the Grunts have had experience with the Elites. This can be ruled out because in Halo 3, Grunts will run from the Arbiter. Another way they could have obtained a higher morale than the Covenant Grunts could be that they are allowed more freedom or a higher status, since they are not bound by the same Covenant heirachy system. They could also have found heresy as a good cause to fight for, and therefore drawn their strength from that, or a combination of this and the fact that they are not constrained by Covenant society. Alternately, they could be better trained and disciplined than Covenant Grunts, or their behavior could simply be the result of their situation. This could be possible as the team that had to research the facility was part of a Special Operations team, which are known for their combat effectiveness and higher confidence and drive. Yet another possibility is that Sesa 'Refumee, the leader of the Heretics, is a particularly charismatic individual (given that the Prophets deemed his heresy to be such a threat) and that he is able to inspire the Grunts to be more dedicated combatants.

It is also important to note that in Halo 3, the Grunts are more courageous than beforehand; fighting more ferociously and are seemingly more hostile to the enemy. In the level Sierra 117 a Marine comments on the fact that even the Grunts weren't pushovers when led by the Brutes. The Arbiter replies that their new found courage is a result of fearing their new Brute masters, who are more cruel and primal than the Elites. Another idea is that the Brutes mixed a gas into the methane tanks to make the Grunts more aggressive, as suggested by a Marine. Also in Halo 3, when a superior ally or many of their allies are killed Grunts have tendencies to ignite two Plasma Grenades and become kamikazes, in this case they let out a strange continuous battle call, and start running towards an enemy with two plasma grenades in-hand. These Grunts are known as "Suicide Grunts" to many gamers and are considered one of the more irritating ways to die.

The intelligence of Grunts has often been hotly debated, as much of the source material contradict one another. In the Eric Nylund novels they have been described as dog-like and animalistic but at rare moments, intelligent, such as the Grunt that inadvertently activates the Nova Bomb. In Halo: The Flood, Grunts are shown to be much more intelligent, pulling off military maneuvers and other actions, such as their attempt to put a grenade into Master Chief's suit and Yayap who has a higher than normal intelligence for a Grunt (though he may have been one of many not mentioned in the novels or games). In game, their battlefield tactics are rather simplistic, but they are more than capable of using a variety of weapons and in Halo 2 and Halo 3 pilot vehicles such as the Ghost. It is also worth considering that as a slave race, they are most likely left untrained and uneducated to make them easy to control. Grunts seem to outnumber the other races to a large degree and might offer impressive resistance if properly organized. Grunts have been called "cannon fodder" because their Elite or Brute leaders will often send them out to serve as a distraction, rather than actually having them effectively engage an enemy in combat.

Nomenclature
Grunts often have simple, easy to pronounce names. Usually including repeated sounds. The most common names will start with a consonant, then a vowel, next a consonant, then the first, and second letters repeated (e.g. Dadab,Yayap). Other names are much simpler, consisting of a single vowel and three consonants (e.g. Flim). Some exceptions have occurred where the name will have more consonants then usual, although if the letters were not repeated, they would be the same as the first method of naming (e.g. Kwassass). Most Grunt names are a combination of the same sounds:
 * Short A.
 * Short I.
 * Y used as a consonant.
 * The consonants D, F, L, K, S, and W.

As mentioned above, Grunts do not have family names. Instead they identify themselves by famous ancestors, their homeworld, and where on that planet they lived.

Anatomy and Physiology
Grunts are 4 feet and 6 inches tall and are relatively weak compared to other Covenant species. Although they can easily walk either upright on two legs, they are often seen using their arms as legs and moving in a quadrupedal fashion. While carrying armaments, they are forced to walk upright so that they may support their weapons with their hands, but while trying to flee, or while patrolling without a weapon drawn, they use their oversize arms as forelegs to add speed or stability to their gait. They are also sometimes described as "Hermit Crabs".

Grunts' forearms are incredibly over-sized, as are their calves, while their upper arms and thighs are incredibly minute. This has allowed them to be quite excellent climbers, as discovered in Halo: Contact Harvest. The only way for them to even be able to move like this is if their biceps and triceps are in their forearms and calves, although why they would evolve like this is unknown. This may, however, have to do with the claws that protrude from some of their joints, as the extra mass would add to the force used when attacking with their claws. They also have very good finger reflexes, as they can fire a plasma pistol at the rate a Elite can with a Plasma Rifle.

Grunts have hooves on their three-toed feet, and their skin is leathery and purple-grey, although Contact Harvest describes them as having a tough exoskeleton. They have a single claw that protrudes from each elbow and knee, but its function is unknown, since there are no known instances where it was used in combat. While they are small, stocky, and are not agile; however, they are quite sturdy, and most may be weak, as they seem to be unable to carry a weapon heavier than a Plasma Rifle, although certain Grunts of higher ranks appear to be surprisingly strong, able to carry an undeployed Plasma Cannon or fire a Fuel Rod Gun without toppling from the recoil. However, physical strength may not actually go along with rank; the types of weapons available to them may be a part of a "thrust" issue with the other Covenant. As rank-and-file Grunts are clumsy and tactically inept, more powerful weapons are likely only issued to those who are more disciplined and experienced.

Grunts have been described as breeding prodigiously in many instances, with large egg clutches and short childhood periods. This might explain why there are so many Grunts on the battlefield. This combined with the large number of young per clutch and rapid sensory motor integration development was one of the primary reasons why the species were given the role of disposable cannon fodder. Their unburdened neural pathway allows them to absorb knowledge more freely compared to their peers. As such, they are constantly monitoring the void for traces of human communication and have developed an understanding of one or two human languages. This was a source of pride and stress to them. The Prolific breeding and rapid development, coupled with the indicated population of 300 million seems to indicate that their population is in an endemic state when they are being killed in masse.

Grunts also have average eyesight and hearing, but they seem to have a very well developed sense of smell, sometimes sniffing the air to detect traces of foes or hidden enemies. . This is facilitated through the olfactory membranes installed in their masks. There are notable differences between the Unggoy of Halo: Combat Evolved and Halo 2, and the Unggoy of Halo 3. Some of the differences of the Halo 3 Grunts are elongated heads, the lack of the elbow claws, red eyes, and a leaner torso. This may be attributed to different races of Grunt. Halo: Combat Evolved is the only game to feature "curl back" armored Grunts. Halo 3 ' s Grunts have grey mottled skin rather then the black, porous skin of the previous games' Grunts. Also, if the player manages to knock off the gas mask worn by the Grunts, a set of whitish-grey teeth can be seen that is somewhat similar to that of Humans'.

Grunts seem to be physically stronger than unaided Marines and are capable of carrying extremely heavy equipments such as the Plasma Cannon and the Fuel Rod Gun, whereas UNSC Marines have trouble. In Halo 3, Grunts can be seen carrying Fuel Rod Cannons with one arm, as well as Plasma Cannons, although they do not use the latter the way Spartans, Brutes and Elites do, instead they try and find a place to mount these massive guns.

Homeworld
The Grunt home world of Balaho is a cold, swampy planet with a methane atmosphere and naturally occurring pillars of fire. The cold nature of their planet makes them highly covet any source of warmth and light they can find, mainly due to the blue death.

Since their natural environment is methane-filled, they have to carry tanks of methane in their environment suits to breathe. Without this breathing apparatus, they will suffocate in an atmosphere which is made up of gases they are unable to breathe. They have also been seen inhabiting large environment domes that have airlocks and methane filters for them to breathe, while not in armor or restocking their methane reserves at Battlefield Methane Tanks. Grunts also have high-pitched and squeaky voices, possibly due to acclimation to prolonged, methane gas exposure. These voices are commonly regarded as humorous by most other races.

Grunts also have thick, luminescent, light-blue blood, possibly a result of methane-based binding proteins in the blood to facilitate methane-based respiration. Horseshoe Crabs also have blood that is very similar in color, it may be that their blood, like the horseshoe crabs, is blue due to copper. They may also go as far as to contain a protein very similar to hemocyanin (copper based) which is the horseshoe crabs equivalent of hemoglobin (iron based). Most grunts will eat a sludge-like substance from something called a Food Nipple. These are believed to have tamed the Grunts after the Unggoy Rebellion. Previously, though, the Grunts fed on meats and vegetables on their native planet.

Furthermore, Grunts are known for their frequent naps, even sleeping in high-risk combat environments, sometimes even in open daylight or immediately after an enemy has retreated. Whether this is a product of their methane-based metabolism, or if they are just lazy, is unknown.

Their home planet was nearly glassed during the Grunt Rebellion.

During the Grunt Rebellion, the Grunts proved to the Prophets that they are stronger in numbers and can be deadly if they are motivated enough.

Overall
The Grunts are the lowest tier of the Covenant rank hierarchy with very few exceptions. An example would be that in the novel by Joseph Staten "Contact Harvest", there is one grunt known as Dadab who is seen as a religious figure known as a Deacon. Deacons are asked to bless food and say prayers for troops before battle, as well as other tasks, indicating there is a small amount of respect for the unggoy from prohpets and higher ranks and that they are important in keeping Covenant religious views to other members strong. They are also known to be bitter rivals with Jackals as they are both on the bottom of the social hierarchy and from a political and military standpoint, are expected to obey the commands of Elites or Brutes without hesitation. This unwavering faithfulness is enforced by the threat of punishment, although on the battlefield, such social protocols are often ignored, where as the Grunt will run in fear as to seeing the Master Chief or the Arbiter or when their leader is killed.

Grunts are subdivided into sub-rankings, lower-ranked Grunts are typically poor combatants, and while higher-ranked Grunts may be formidable adversaries in combat and even show signs of leadership capability as well as bravery. A good way to see that low-ranked Grunts are poor fighters is that most Grunts who sleep on duty are Minors. In groups they can be deadly as well as tenacious (but it depends on the level of difficulty), especially if they have an Elite or Brute commander. The Unggoy are also considered to be somewhat humerous by other species, like Jiralhanae, humans and Sangheili for their small stature and squeaky voices.

Rank Structure
Grunts have five classes which are easily identifiable by the color of their armor:

Other ranks
Deacon: The only position open to the Grunts in the Ministry of Tranquility. This rank doesn't involve combat or hard manual labor, though they have been known to carry around Plasma Pistols, possibly meaning it is the lowest position on the Covenant hierarchy. But as seen in Halo: Contact Harvest the Deacon ordered around other Unggoy whenever it came to matter of religion.

Cylindrical-backed Grunts It was in concept art for Halo: Combat Evolved and was seen again in a Halo Wars screen shot on The Halo Wars official Website. They are also seen in the Halo Graphic Novel, in the story The Last Voyage of the Infinite Succor. They are seen at the start of the story, putting out a fire, and being ambushed by the Flood. Some of them also accompanied a squad of Elites on the Infinite Succor.

Curl-Back Grunts: In Halo: Combat Evolved, there was an alternate suit for the Grunt Infantry. It was a slightly larger mask that covered more of the face and a methane tank that curled upwards instead of it sticking out. The reason for this is because they could roll out of Spirit dropships, possibly to take cover and to get out of the ships faster as this variation is only seen in Halo: Combat Evolved. It is possible that the curl-back design would denote that the wearer was a Grunt Heavy. This could have been used before an actual rank and suit were made for the Heavy Grunts. This is supported by the fact that most Turrets in Halo: Combat Evolved are controlled by curl-backs (on higher difficulties), and that there are screenshots depicting them on turrets in Halo Wars. But if the player looks closely, he/she will find that ALL Grunt ranks on Halo: Combat Evolved have this armor design, including Minor Grunts, Major Grunts and Spec Ops Grunts. Also some people think that the methane tanks on the "Curl-Back Grunts" could have not been refilled unlike the other grunts methane tanks in the Halo series. Curl-back design could also be a type of out-dated suit that was slowly being removed from the Grunt military. The reason for the curl-back methane tank is that it was in fact, a different version, which would contract for easier transportation as it ran out of methane.

Combat
Grunts usually fight in groups consisting of mostly Minor Grunts, one or two Major Grunts, and an Elite leading them in Halo 2 or a Brute in Halo 3. Most of the time, when the Elite or Brute leading them is dead, the Grunts will run away, even the higher-ranking ones. If playing on the lower difficulties (Easy, Normal) Grunts may run away even if they just see you. Although, Minor Grunts will sometimes regroup and attack you. If the Brute or Elite leading them is dead, but the Major Grunts aren't, some Grunts will stay and fight because they will have someone leading them. Grunts can be tenacious fighters as long as they have someone leading them. Higher-ranking Grunts may not run away, but keep fighting you.

Weaponry
Grunts are often armed with the ubiquitous Plasma Pistol, although they are sometimes seen wielding Needlers and Plasma Rifles. Sometimes grunts will carry Fuel Rod Gun but the size shrinks a little when they wield it.. Grunts can be dangerous in groups, even if they are mostly Minors, as they usually wield Plasma Pistols, which can deplete your shields quickly if many are firing at you. Grunts are never seen equipped with two-handed weapons like Covenant Carbines, Brute Shots, Beam rifles, etc. Grunt Heavies can carry folded Plasma cannons. Special Operations grunts and Grunt Heavies are occasionally seen bearing Fuel Rod Guns. In Halo 3, they can be seen carrying Fuel Rod Guns with one arm but they use both hands most of the time since it is such a powerful weapon, as well as the Plasma Cannon, but they do not use them in that manner, and instead they run and try to find a place to put it so they can get out of the fight quicker. On The Storm and The Ark, a Grunt can be seen with a Brute Spiker. On The Ark, it is a Grunt Heavy that is walking alone on the top of the tunnel, which the Human vehicles, including 3 Scorpion Tanks, come out of just before the Scarab battle.

All Grunts are equipped with and often use Plasma Grenades and sometimes Spike Grenades, although Ultra Grunts, Special Operations Grunts and Major Grunts throw grenades in combat more often. Special Operations Grunts also use Fuel Rod Guns in combat. They have been known to "'Nade Spam'" Plasma Grenades on the Legendary difficulty, which means that in a group of 10 Grunts, as many as 8 of them will throw Plasma Grenades, one after the other, in an attempt to easily dispatch their foes. In Halo 3, Grunts who are startled or possibly see their allies get killed will arm 2 Plasma Grenades and rush to the player, causing an explosion after a few seconds. This is an action of desperation or fear, and Grunts using this choice of action are preferably "last-minute Kamikaze". If there are more than one charging at you, shoot the first one; as the other Grunts run past, the dead Grunts grenades will detonate, killing the rest. As mentioned earlier, most Grunts are inaccurate shooters, with the exception of Ultra Grunts and Special Operations Grunts, which pose more of a threat with their very accurate marksmanship and their tendency to throw grenades accurately. They are never limited in skill when using heavy weapons either.

The weapon most commonly used by Grunts seems to be the Plasma Pistol, however, the Needler is a close second. Grunts prefer Needlers over Plasma Pistols and Plasma Rifles, the standard weapons issued to them. It is also possible for a Grunt to wield a Brute Spiker. A Grunt will usually resent being given a weaker weapon in place of the one they are currently wielding, and this will cause the Grunt to get very upset; they will pound their "fists" on the ground in a temper tantrum and might say something opposed to switching out the weapon. For example, if you give a Grunt a Fuel Rod Gun it will say "me not worthy" and bow. This comical behavior can also be associated with impatience or excitement.

On the level Uprising, Grunt teammates can be equipped with the Human Rocket Launcher, but the size of the Rocket Launcher shrinks a little. Sometimes Grunts can wield a Heavy Machine Gun.

Grunts do not only wield Covenant weapons but you can give them Human weapons on levels such as Sacred Icon you can give them the Human Magnum and SMG by dead Flood Combat Forms.

A single Grunt is also heard of using an Assault Rifle in the Halo Graphic Novel.

Overall in Combat
The Grunt can use any sort of weapon that is designed to be held in one hand. In some situations grunts have been seen to use heavy artillery weapons, such as the Fuel Rod Gun. So, on higher difficulties, the Grunt can prove to be a dangerous enemy to the Player and his/her allies.

Turrets/Vehicles
In Halo: Combat Evolved, Minor and Major Grunts are the primary operators of the stationary Shade Turrets, although the turrets are open to use by other races if a turret is vacant. In Halo 2 and Halo 3, it is the specific task of Heavy Grunts to man Plasma Cannons or Shielded Plasma Turrets, yet if no Heavy Grunts are available, Minor or Major Grunts will often man the turret instead.

In both Halo: Combat Evolved and Halo 2, if a turret operator is killed, nearby Grunts will move to man the unmanned cannon.

Grunts are also surprisingly capable with vehicles, and can man a variety of Covenant ground vehicles:


 * Ghost Halo 2 and Halo 3
 * Shadow (Seen in Halo 2 E3 Demo, have animation but not used in Halo 2)
 * Shade (Halo: Combat Evolved, Halo 3)
 * Shielded Plasma Cannon (Halo 2)
 * Plasma Cannon (Halo 2, Halo 3)
 * Heavy Machine Gun, Halo 3 specifically Crows Nest.

Combating Grunts
Grunts are the most commonly encountered enemy in the Halo series, and are lightly armored and lack any form of additional shielding. In battle, most weapons easily dispatch them. Weapons such as the M6D Pistol and BR55 Battle Rifle are very effective in executing headshots. Like many other unshielded enemies, a single headshot from any gun on any difficulty will kill them (though there are some guns that for reasons unknown cannot execute headshots). Grunts are also easily killed with brief bursts of automatic fire from weapons such as the Assault Rifle, SMG, and the Plasma Rifle. If just out of melee range, the player may fire a quick burst, as the Grunt reels from the hit, the player can melee the Grunt. Some players prefer to melee Grunts to death, and save ammo for Brutes, Elites, and any other foe. Ultra Grunts and Special Operations Grunts have stronger body armor and can withstand more damage than lower-ranking Grunts. Melee attacks generally kill Grunts in one or two blows. They can prove to be stealthy choices of action when clearing out sleeping Grunts, especially if you want to avoid detection. In Halo 3, an attack will sometimes blow off the flimsy cover of a Grunts methane tank, and may rupture the tank inside. The respirator can also be knocked off, which is fatal after a certain amount of time. Even after the respirator has been knocked off they will continue to fight. A leakage of methane gas can turn a situation perilous in the presence of a flame.

Because Grunts often fight in tight formations, grenades and Rockets can be used to great effect. Spikers can also work to a great effect also, as can kill a Grunt with a few shots. However, when stuck with Plasma Grenades, Grunts will panic and start running in random directions, posing a threat to both the player and their allies. It may be heard that the Grunt, when stuck by a Plasma or Spike grenade, he may yell, "Noooooo!", "Pull it off!", "Not again!", or even "Eeeiiiaaayyyhhh!". However, sticking them is particularly useful, as the stuck Grunt will often run towards its comrades, decimating an entire squad at times.

Suicide Grunts
A Suicide Grunt, also known as a "Kamikaze Grunt", is like a "berserk" mode for the Unggoy in Halo 3. Occasionally, an Unggoy will hold two Plasma Grenades in each hand while screaming in rage and charge towards enemy forces. This is usually triggered by their leader being killed, and you can sometimes hear them scream, "For the Great Journey!" or "Witness my beliefs!", "For the Covenant!", "Follow the light my brothers!", "Please enjoy my BRIGHT! BLUE! BALLS!", "*hums the Halo Theme Song*", and rarely "Oh! I bet I can stick him!", but most of the time, they start shouting unintelligible Suicide Terrorists words like "iiiyyyeee yyyeeaattteee", or a simple, but sharp "ooottt!!." Most of the intelligible words are of the former of quotes seeming to indicate that they deeply believe and follow the Prophets and the Covenant religion. Although, some of them are just for humor. They will sometimes not say anything at all and babble pointlessly while running at you, but sometimes they might say something when one gets close to you like "Faith and devotion!" This mode can be achieved by any Unggoy, so it is most likely a parallel to the Brute berserk mode, although Brutes tend to go bloodthirsty, while the Grunts become suicidal, and the Grunts don't do it nearly as often as Brutes do. It tends to happen to Brutes mostly when their leader is slain, when you shoot them enough to make their armor come off, or if you kill their leader in a brutal way (such as sticking one with a grenade). An odd thing about Kamikaze Grunt is that when you throw a plasma grenade it lasts about 4 seconds, when Kamikaze Grunts stick two plasma grenades to their hands they can last over 5 seconds. To see more Kamikaze Grunts more often, activate the skulls Famine and Tough Luck, as observed with one players encounter with a whole swarm of them going suicide. A good way to deal with a swarm of these Grunts is to kill one and by the time next Suicide Grunt comes the fallen grenades will explode, killing that Grunt and the rest of them.

Combat
Suicide Grunts can be VERY dangerous if not taken care of quickly. To locate and avoid being killed by them it is advisable to take the following three precautions. First, keep an eye out for them - they are usually quite easy to spot since they have a blue glow on each side of them. Second, listen for the Kamikaze Grunts' distinctive screams. This is helpful when you are not using your Motion Tracker. Finally, do not wait for them to explode on their own. The grenades won't explode until the Grunt wielding them is killed. Once the Grunt is killed, the grenades will fall to the ground and detonate, destroying anything in the blast radius of the grenades. This can often be used to your advantage. If there are enemies near by, they may be caught in the blast radius. Be careful though, for the explosion may set off stray grenades lying around on the floor. Often Kamikaze Grunts can be a threat if you are sniping and don't hear the screams. Often, these Kamikaze Grunts are, on higher difficulties, lower ranks, such as the Grunt Minor. It is unknown as to why this is, possibly the fact being that higher ranking Grunts on higher difficulties can prove to be even more dangerous when they don't Kamikaze you and simply use the weapons and tactics they already have, or maybe the lower ranking Grunts do this thinking that this is their only chance of stopping the player from advancing any further. Also, when you play Halo: CE, or Halo 2 as the Chief, kill the Elite that is leading them. Up to Heroic Mode, they will break ranks and run. When they do that, take your Assault Rifle in Halo: CE or Halo 3 and mow them down, or use your SMG in Halo 2 to tear them apart, frag grenades are also very efficient at taking them out when they are in large groups.

Trivia

 * Grunts cannot hijack vehicles.
 * Grunts do have a melee animation, but it is almost never used. It is sometimes used to move metal debris out of the way.
 * Grunt's melee animation is similar to the Hunter's.
 * In Halo 1 this is quite funny but when an Elite tries to melee you if you dodge they will often kill a grunt.
 * Grunts are referred to as "cute" by many players, but in Halo 3, they are referred to as "ugly".
 * Grunts are considered to be the comic relief of the series due to their high-pitched voices and high propensity for humorous combat dialogue, short stature both physically and in Covenant society, and their somewhat extreme cowardice on the battlefield.
 * SMGs can normally take a Grunt's methane face mask off in a few shots, showing the Grunt's true face.
 * Unggoy means monkey in Tagalog, which is the Filipino language.
 * The most commonly used weapon utilized by grunts is the famous Plasma Pistol, the second most common being the Needler. Their least commonly used weapon is the Brute Spiker.
 * The grunts' methane masks in Halo 3 look very similar to modern-day gas masks.
 * The Grunt action figure is one of the rarest action figures.
 * The Grunt action figure comes in two colors, green and orange.
 * The methane tank on the back of a grunt will explode when shot at, but sometimes the Grunt won't die.
 * A "grunt" is also a term used in real life military that is slang for infantrymen.
 * A Grunt's Mask can be shot off, but the Grunt sometimes won't die, even though they can't breathe without it.
 * The grunts are one of the weakest enemies you face.

Quotes
A List of Grunts quotes can be found here.