Which way is the dancer turning?
Well, whichever way you thought she was going, you're only half right.
See here for an explanation...
I stared at her for a while and couldn't for the life of me see how she could go any way other then clockwise. I then called G up to look at it. "Oh, she's going clockwise," he said. "No, just a minute -- anti-clockwise." After staring for a few seconds he said, "She goes whichever way I want. It's easy to change."
Eventually, she flipped directions, but the moment I stopped concentrating, she went back to clockwise again. With practice I might be able to get the anti-clockwise rotation more reliably, but it seems to mean that, as I've always suspected, I am very right-brained.