Elite helmet glitch
From Halopedia, the Halo wiki
There is a glitch with the helmet of various Elite corpses in Halo 3.
At the end of the level Floodgate, when entering the crashed Flood ship, a player will find several dead Elites corpse lying around. Some of them have a strange cross-helmet that appears to be a blending of an Assault helmet and a Combat helmet. It appears that the game had attempted to render both helmets on the head of the Elite, and thus, both appear, overlapping one another.
Some speculate is that in the same crashed ship, bodies resembling Rtas 'Vadum (Half-Jaw) appear randomly which happen to be wearing Combat helmets, and that the Elite was wearing an Assault Armour helmet, and the game programming attempted to change the body into the Half-Jaw version.
