Why Is A Cat Able To See In The Dark?

First a cat cannot see in pitch dark. It can only see in dim light than you can. You can see in very bright light, and also in dim light. If you come out of a rather dark room where you saw well enough not to bump into things, into strong sunshine, you have to shade your eyes a moment until the pupils become smaller and admit less light. Going from brightness to dimness, you can see better after the pupils of the eyes have had time to expand. It can shut out light if there is too much, or open up to admit all the possible rays if the light is too dim. The pupils of the cat's eyes are able to close like narrow slits in a shutter, to keep out the noon-glare of the sun; and to expand to a big round window that catches all the rays in semi-darkness. They sleep and rest in the daytime, and hunt their prey at night. The house cat hunts mice at night. So a cat needs eyes that are veiled from strong light by day, and that can expand to admit all the few rays of light that are abroad at night.