Suicide Grunt

A Kamikaze Grunt is a sort of "berserk" mode for the Unggoy in Halo 3. Occasionally, an Unggoy will prime one Type-1 Antipersonnel Grenade, also known as a "Plasma Grenade", in each hand and charge towards enemy forces. This mode can be achieved by any Grunt, so it is most likely a parallel to the Jiralhanae's beserk mode.

Combat
Kamikaze Grunts can be a large threat if not taken care of quickly. To locate and avoid be killed them you can do three things; first, keep an eye out for them because they will usually be quite easy to spot since they will have a blue glow on each side of them. Second, listen for them when the Kamikaze Grunts will start screaming and yelling, and this can help you since sometimes be you'll be in zoom mode or they will be coming up behind you. And finally, do not wait for them to explode on their own. After you've killed the threat, the grenades will fall to the ground and detonate, destroying anything in the blast radius of the grenades.

Trivia

 * The name is derived from kamikaze tokubetsu kōgeki tai, Japanese suicide attackers from WWII.