Urinating Brute

On the level "The Ark", when you reach the room with sleeping Grunts after destroying the Scarab, by the door you go to through to continue farther in the level there is a Brute taking a "break" in the corner. He originally has his hands in front of him, but after a short time he will move his hands behind his head and then shake the excess urine off. After a while it will move into the main hallway and get into position waiting for intruders. If it notices you it instantly goes into attack mode.

The best way to see this is to start The Ark on Rally Point Bravo go straight and then look at the right corner of the room. If you play the whole level when 343 Guilty Spark stings the curious marine go into that room and do what is described just above. It is often advisable to kill the marines who accompany you as they often alert the grunts or brute which means you don't have a chance to watch this brute "take a break".

Trivia

 * It carries a Brute Spiker.
 * If you look at the walls and the floor after he is done you can see what he has left behind.
 * The rank varies depending on the difficulty.
 * If you watch him for a bit a voice will send you a message saying "Chief, tap him out". The gender of the voice varies depending on the difficulty also.

Link to the video here.