Look at these balls. Your eyes tell you that they are different colors, but a closer look will show that the balls are all the same color: brown. But they all have different colored stripes, and anyone who carefully shops for clothing will tell you that stripes make all the difference in the world. This is a Munker illusion from David Novick, engineering professor at the University of Texas at El Paso. He explains how a Munker illusion works here. You can see the balls without their stripes in another image, or just watch this animation of the balls changing from stripes to no stripes.