A close up image of a blue and brown iridescent cuttlefish next to some leafy green foliage. The cuttlefish's w-shaped pupil is seen in the center of the image. . It's easy to think of pupils as simple holes that widen in the dark and shrink in the light. But if you look across the animal kingdom, you'll see a variety of pupil shapes: vertical slits in cats and snakes, horizontal rectangles in goats and horses, and W-shaped crescents in cuttlefish, for instance.