If you have ever shined a flashlight into the woods at night and seen a pair of glowing eyes staring back at you, you have witnessed one of evolution's most brilliant optical engineering feats. That eerie glow is not a trick of the light; it is the Tapetum Lucidum, a microscopic mirror hidden just behind the retina. This biological retroreflector bounces photons back through the visual cortex a second time, effectively doubling the light available to nocturnal predators like wolves, cats, ...