Rtas 'Vadum in crashed Flood ship

The Half-Jaw in crashed Flood ship easter egg can be found on the level Floodgate. When you jump down the hole to get into the Flood ship that crashed, there will be a few dead Ultra Elites lying around. The first one you see has SOMETIMES Rtas Vadum's (Half-Jaw)face. However it is the old model from Halo 2. You can get it infected to if you push it down the hole and release some infecton forms.

http://img119.imageshack.us/img119/2048/13829028mediumhw4.jpg

Note: This may be a normal Elite missing a jaw!