The human brain works in mysterious ways. Optical illusions don't occur because of your eyes, they occur when your brain misinterprets information your eyes send it. An illusion is "a mismatch between the immediate visual impression and the actual properties of the object," according to vision scientist Michael Bach.
Everything that enters the senses needs to be interpreted through the brain, and sometimes your brain gets things wrong. So, what do you see when you look at the below image?
Most people see a gorilla walking across a beach. It's actually a man bending over to unhook a fish he just caught.
Don't worry, you weren't the only one to see a gorilla. In fact, people had to make a concerted effort in order to see something that wasn't a gorilla (yes, it's actual work to see what this is a photo of). As one redditor wrote, "Man, I had to put in work for this... I had to zoom in, look at a few things, the whole process was about 10 secs, but I was fooled." Another had an easier time seeing what was going on when he realized there was something coming out of the gorilla's behind: An older white man wearing sunglasses.
Others weren't so easily fooled. As with anything of this nature, there had to pretentious people who made it clear that they knew what was going on along, because what's some good-natured, optical fun without a superiority complex? "It took me so long to finally see the gorilla! That's a really good one," one wrote. Another added, "For once I saw what the picture actually was before I saw what it looks like."
What did you see?