Optical illusions can mess with your mind and make you think you're seeing things that aren't there. That's what is so cool about most of them. This collection of pictures and gifs will feel like P90x for your brain.
There are three types of optical illusions: literal, physiological, and cognitive. Ambiguous illusions are pictures or objects that elicit a perceptual "switch" between the alternative interpretations. The man's face is also an example of one. Physiological illusions are the pictures that appear to be moving. These are caused by bright colors leaving what's called an "afterimage" in your brain. The optical illusions pictured in this gallery are not moving, yet they seem like they're animated. That's an example of a physiological illusion. From pink circles turning green to an eyeball that looks like a sink drain, what you think makes sense doesn't really at all. These are eye tricks at their finest!
Just be sure to give your eyes a break while looking at these. You know that old saying, right? If you look at one too long your eyes might stay that way! Or wait, is that crossing your eyes?