Had some very shiny eyes:

Recently, researchers found these mammals…have a unique way of coping with extremely dark Arctic winters: Their eyes change color.

During the sunny time in their habitat, reindeer have yellowish-gold eyes, but during the cold season, the eyes turn a noticeable hue of blue, a new study published in the Proceedings of the Royal Society B reported.

It’s because of changes in a light-reflecting tissue layer behind the retina, according to Science. “This structure, called the tapetum lucidum (Latin for ”˜bright tapestry’), gives the eye’s light-sensitive neurons a second chance to detect scarce photons in low-light conditions. (The layer also produces the ”˜eye shine’ that can make animal eyes appear to glow in the dark.)” In other words, it makes the eyes extremely sensitive to light.

This photo, which accompanied the article, does not show the blue eyes. But at least it’s a reindeer, looking rather nonplussed: