Cavemen
From Halopedia, the Halo wiki
On the Halo 3 level, "Sierra 117", you can find a family of cavemen with Marcus Lehto's face.
Guide
To find the family of Caveman (or monkeys as some people call them), go past the point where Johnson's says his Pelican got shot down. You will see a concrete column with the number 3 on it. When you stay beside the left wall and go as high as you can, you must turn around and you will see the cavemen against the wall. The largest of them is holding a teddy bear. Although you can try to shoot them, a death animation for them has not been made, so they will remain idle if you try to kill them, though blood will still spurt out.
<youtube>FrAjTwinQkU</youtube>