Optical Illusion: The Spinning Dancer

It's a moving .gif file, so I can't post it here on the blog, but here is the link to it:

The Truth About the Spinning Dancer

[...] The silhouette image of the spinning dancer doesn’t have any depth cues. As a result, your eyes will sometimes see the dancer standing on her left leg and spinning to the right. And sometimes they will perceive her as standing on her right leg and spinning to the left. Most people, if they stare at the image long enough, will eventually see her turn both ways. [...]

I couldn't see the flip at first, but then happened if I stared at her lowest foot, or looked at the image from my peripheral vision. Too weird.

This has been a popular email attachment, apparently. The article discusses the illusion and it's relation to vision, and has some links to other illusions, too.