Which way is this dancer spinning? My natural inclination is to say counter-clockwise, but I can actually get her to reverse direction pretty easily. The trick is to look away – not away completely, but just enough so that the image is in the corner of your eye. Then, while she’s still spinning in your peripheral vision, think about the leg going in front of the body where it used to be behind, or vice versa, and get into that “rhythm” for several revolutions before looking back. The first few times I found that I’d see her going clockwise just for a moment before she’d snap back to counter-clockwise, then I actually got her stuck going clockwise for a while, but then I could pretty much change direction at will in just a few seconds. I’d love to know what an fMRI scan would show while I’m doing that.

(Hat tip: Freakonomics blog.)