I’ve always found this fascinating. It’s fun too, once you get used to switching between your left and right brains so you see the girl spinning alternate ways. By default, I usually start off seeing the girl spinning to the right (right brain at work). Then if I read the text below the image, I can see the girl spinning to the left as my focus leaves the image, and my left brain is at work comprehending the text.
Try it. It’s fun!
Instructions: Look at the spinning woman. If she is turning right, the right side of your brain is working. If she is turning left, the left side of your brain is working. If she turns both ways for you, then you have an IQ of 160 or better. <– Don’t know about this last claim. Would be great if it’s true, but I somehow doubt it… 😛