Optical illusions are cool. Every once in a while, an illusion goes viral on the internet and it confuses the whole world, like the brick wall illusion and kind of like that dress.

Some of these illusions are more difficult to figure out than others. Some just take a second look, and others need a whole explanation.

Illusions are created when someone takes a photo at the perfect timing, and something in that photo is just a little off, which makes the whole thing a little funky. While there are always the classic illusions, illustrated ones and photographs that circulate online, there are tons more to be seen all around the web, and the are quite a few places to go to see all of the most mind-boggling images from around the world.

Here are just 15 strange images that may need a second glance, or third or fourth, to really figure out what's going on in them.