* bends over and draws a quick, simple outline of one in the dirt-- the lids, and two concentric circles. *
This part in the middle, here-- that's usually a black dot or a circle, right? That's the pupil. The size of it changes according to how much light the eye's being exposed to. If it's dim, it grows bigger to try and direct more light into the eyeball. If it's bright, it shrinks so there isn't too much of the same.