Why Cat Eyes Have Vertical Pupils

In an optical TED-Ed lesson written by Emma Bryce and animated by Ivan Tamas, narrator Alexandra Panzer explains why cat eyes have vertical pupils. She also further describes the variety of pupil shapes and sizes throughout the animal kingdom, including those of humans.

Peering into the eyes of different animals, you'll see some extraordinarily shaped pupils. House cats, for one, are twilight hunters with vertically elongated pupils. Many grazing animals, like goats, have rectangular pupils. Other animals have crescent- or heart-shaped pupils. So, what's going on?