A black cat's eyes may frighten in the dark, but that glow is helping the felines see better, NPR reports. When light fails to enter their brain, cats, dogs, and other animals bounce the light back with a reflective surface on the eye. That gives the light a second chance to shine in. Why the color variety? Substances like riboflavin and zinc determine whether the eye shines schnauzer turquoise or kitty-cat green.