Tapetum lucidum

This cat's tapetum lucidum makes its eyes flash yellow in a photograph

The tapetum lucidum (Latin: "bright carpet") is a reflecting layer behind the retina of the eye; it serves to reflect the light back to the retina, improving vision particulary in low light conditions. It is found in many animals, particularly nocturnal animals with good night vision, such as cats. It is responsible for the feline equivalent of the red-eye effect, causing cats' eyes in flash photographs to take on a wide variety of colours including blue, green, and yellow.

Bottlenose Dolphins also have a tapetum lucidum. Humans do not.