http://www.lostinbrittany.org/dotclear/images/2007-07/spinning-silhouette-ms2007aa.gif

Normally you should see this shade turning clockwise.
But if you concentrate enough, on the background or the foot's shade, and THINK it can turn counter-clockwise... It will!
Of course you can make it turn clockwise again.
Amazing!

And it's just a gif, so if anyone knows how it works... :)

At first I couldn't stop seeing it go clockwise, now I can't stop my mind from seeing it go counter clockwise.

I saw it counter clockwise to start out with

counter clockwise from the start for me

same and couldnt get it to go clockwise

It seems easiest to switch by looking at her foot and its shadow, not focusing very hard.

At first I couldn't see anything; it was only spinning clockwise. Then it started spinning counter clockwise and that was all I could see. Then I found that if I stared at the foot long enough it would start spinning the other way. Nifty.

I had to consciously tell myself that the foot was in front when going either left to right or right to left, in order to made the silhouette appear to change directions. I tried to make the dancer change directions as quickly as I could. It was frustrating at first, but now I can mentally make the dancer change directions every few seconds.

It seems like no matter which direction the dancer is spinning, the pony tail is pointing in the wrong direction, though!

Trying to find some explanation, I found this illusion (http://www.michaelbach.de/ot/mot_motionBinding/index.html), along with many more, but this one is the perfect example of how easily our brains can be abused.
Stunning.

All I keep looking at is the boobies.... what is the trick if you do that?

I think everyone saw it going counter first is because they were reading what you wrote while looking at the picture with their perpheral vision (not looking directly at picture). When you look at it directly it changes.

It was fun to play with..lol

I'm unable to see it going counter-clockwise at all.

I can get it to change back and forth pretty rapidly now. It starts going clockwise, or should for most people since when it loads up, the foot is at the right moving towards the left. The way I can get it to switch quickly is, I stare at the foot and then it goes counterclockwise, almost instantaneously. If I want it to go clockwise, I blink right as the foot gets to the right side right as it starts moving left. That makes it go clockwise for me.

I thinks a scam, i couldnt get it to go CCW to save my life, then when it finally did i blinked sat up straight and rubbed my eyes (usually works to reset optical illusions) and was still going CCW for about 15 more seconds. then it abruptly reverted!

I watched it before reading.