The tapetum lucidum (Latin: "bright tapestry", plural tapeta lucida) is a layer of tissue in the eye of many vertebrate animals, that lies immediately behind or sometimes within the retina. It reflects visible light back through the retina, increasing the light available to the photoreceptors.
The tapetum lucidum contributes to the superior night vision of some animals. Many of these animals are nocturnal, especially carnivores that hunt their prey at night, while others are deep sea animals. Eyeshine is a visible effect of the tapetum lucidum.
When a light is shined into the eye of an animal having a tapetum lucidum, the pupil appears to glow. Eyeshine can be seen in many animals, in nature and in flash photographs. In low light, a hand-held flashlight is sufficient to produce eyeshine that is highly visible to humans (despite our inferior night vision); this technique, spotlighting, is used by naturalists and hunters to search for animals at night. Eyeshine occurs in a wide variety of colors including white, blue, green, yellow, pink and red.
I took a very cool photo of a red-eyed wild animal myself :p i'll post it later!