Anyone who has taken a flash photo of their cat is aware of the cloudy yellow/green reflection in their eyes. Such was a topic of discussion on Flickr Technique.
The reason for this is that cat eyes have a reflective coating in the back of their eyes called the tapetum. Nocturnal animals have this so that light passes twice through the transparent rods/cones of their eyes creating a second opportunity to absorb the photos and resulting in better night vision—at the price of some acuity of vision because of the folded optical path. Light comes from two distances and cats are far-sighted anyways.
Pretty neat piece of evolutionary engineering.Continue reading about red eye in photography after the jump.