That eye belongs to an alligator.

An alligator has two sets of eyelids. The outer set works the same way as a human’s eyelids — closing from the top down and the bottom up. But an alligator’s clear, inner eyelids — called nictitating membranes — close from side to side. An alligator will sometimes close just its inner eyelids while swimming so that it can see underwater while still protecting its eyes.