Sea Snake
From Tomb Raider Wiki
The Sea Snake is a grotesquely overgrown eel that inhabits a cavern underneath the ship in the Living Quarters. Much like the Moray Eels it will lunge out of its chosen hiding place and snap at anything in its reach. It swings its head from side to side, snapping while it does so to try to catch its prey. Only one or two bites is sufficient to kill Lara, and it cannot be killed. Do not underestimate it. Fortunately, it will not leave its home to pursue Lara.
