If your friend plays a trick on you, you're well within your rights to not hang out with them again. When it's your eyes playing tricks on you, you have to put up with them. They're an integral part of the whole "being able to see" thing. Luckily, the tricky nature of these pictures is also what makes them fun. I'd rather discover that a human woman does not have a dog's head then go the rest of my life believing so, all after a few seconds of staring. Your peepers may mess around with you when it comes to...