cat eyeshine

Cats are weird. Sometimes they are funny weird. Sometimes they’re annoying weird. And once in a while, they are scary weird. Like attempting-a-home-invasion-while-appearing-demonically-possessed weird.

The cat who starred in a viral post Thursday on Reddit’s r/wtf subreddit was the third kind of weird. In the post, which received over 37,000 upvotes at time of writing, user Jaygoon shared a video of an unfamiliar cat rapidly pawing at the front door like Daniel from the Karate Kid practicing his fence-painting technique. Aside from the attempted feline B and E, the most alarming thing about this video is the bright glow emanating from the cat’s eyes. They look like kind of like spotlights, or a window into the world’s purest soul.

Most cat owners are likely familiar with this phenomenon, called “eyeshine.” Your pet is being cute, and it’s dark, and you try to snap a quick photo of them only to have it look like the kitten spawn of satan.

Turns out there’s a perfectly rational, scientific explanation behind eyeshine and it has nothing to do with the cat playing with a ouija board it found in the basement. Along with a host of other nocturnal animals, cats have a layer of tissue called the tapetum lucium located behind their retinas. The tapetum lucium acts like a mirror, reflecting light and allowing the cat to see in poorly lit circumstances as if it was shining a flashlight on the scene.

Humans don’t have a tapetum lucium, which is why our eyes don’t have a hellish glow to them at night. From an evolutionary perspective, there’s no reason for us to have one, because our eyes adapted for daylight vision.

cat
Spooky!

But even without the reflective layer, humans sometimes get eyeshine from flash photography. That’s just because a camera flash is really bright, as it’s designed to reflect off the subjects. In people, however, eyeshine is typically red. When light enters the retina and bounces back outward, it passes through blood vessels in the eye — the blood filters the reflecting light, coloring it red.

Sometimes animals have colored eyeshine as well. Usually, it’s a shade of green, but some species have yellow eyeshine and blue-eyed animals sometimes have the same red-eye effect as humans.

So if you’re cat is looking all evil, don’t worry. It’s probably just upset because you’re shining a light in its face.

Photos via Jaygoon/Reddit, Wikimedia