Tapetum Lucidum

What causes that eerie yellow glow when you shine a light at your dog's eyes? Or causes the eyes of your pet to turn out as bright yellow spots in photographs?

It's called a Tapetum Lucidum, and it's the membrane that lines the back of the lens in your dog's eyes. This reflective structure acts like a mirror and reflects light back through the retina, giving the retina two chances to catch the light. Most animals that are active at night have Tapetums to improve their night vision.

You can best see the effect when the pupils are completely dilated.