If you had the kind of family members who liked to pull coins out from behind your ear and trick you into thinking their thumb had fallen off, you’ve probably come across this weird optical illusion before. If you take a roll of paper and look through it with one eye whilst staring at your hand with another, it looks like a hole has been cut out of your hand.
But what is actually happening here? Braincraft’s Vanessa Hill explains that the illusion is caused by something called binocular rivalry. “Two different images are being shown to each of your eyes. If your brain can’t combine these two images, it just suppresses the image in one eye and your other eye becomes more dominant,” she said. “In this case your hand will generally stay suppressed from your awareness because it’s the weakest stimulus.”
Babysitting pro tip: this illusion provides endless hours of entertainment for kids who are gullible enough to believe that they actually have a hole in their hand. It’s also a good way to subtly spy on your work crush from across the office, although I refuse to accept responsibility for any restraining orders acquired through this method.