Human beings have round pupils; cats have pupils shaped like vertical slits. What’s the advantage for cats and people, respectively, in those different pupil shapes? Different pupil shapes seem to be an adaptation to different activity patterns during a 24-hour day. Cats belong to the category of nocturnal animals, who do most of their foraging for food at night. Other nocturnal animals include rats, bats, mice, flying squirrels, and owls. These animals rely heavily on hearing and touch to get around, but they also have the ability to see in very dim light. Their eyes have big lenses and sensitive retinas. But many nocturnal animals, such as cats, are not strictly nocturnal — they move around during the day as well as at night. They need some way to protect their sensitive eyes in daylight, and slit pupils provide that protection.