Cat Eyes: Why Do They Glow in the Dark?

Many animals that hunt at night, like cats, dogs, and owls, have a special layer behind their retinas. This layer acts like a tiny, high-tech mirror. When a tiny bit of light enters a cat's eye, it passes through the sensing cells, hits this mirror, and bounces back for a second pass. This gives the cat a 'second chance' to see using the exact same light!

When you shine a flashlight or take a photo of a cat at night, you see a brilliant glow. This isn't the cat making its own light; it's your light bouncing off that mirror layer and straight back at you. Depending on the minerals in the mirror, the glow can look green, yellow, or even bright blue.

To make the most of their 'eye mirrors,' cats also have pupils that can open much wider than ours. In the dark, a cat's pupil becomes a giant circle to let in every possible scrap of light. During the day, they shrink into tiny slits to protect their sensitive 'night mirrors' from being overwhelmed by the bright sun.