Think about a word, any word. Take, for example, moist. Now, say that word over and over and over again in your head. There's something really weird about it, isn't there? Something that you can't just wrap your head around. Suffice to say, you'll never think about it the same way again.
There's also a similar phenomenon when it comes to certain pictures. You thought you saw it clearly, but then someone points out something incredibly weird about it. Something you never noticed before and now, you can't get that image out of your head. Don't know what we're talking about? No worries, just take a look at these 20 pictures and we'll guarantee that they'll simply leave you in disbelief.