Face on Gravemind

On the level Gravemind,there is what looks like a crocodiles face.

To see it,play the level on any difficulty to the second part where you are outside.(The place where the spec-ops grunt is carrying the fuel rod cannon (it's not where the angry skull is but a place like it)).Go out the door and kill the Brute,the Jackal and the Elite,then go to where the sniper was before you mauled him with whatever weapon you had,then turn around.On the wall beside the door you came out of,should be what I think is a crocodile with something in its mouth.