Optical illusion

For a while, there's been an optical illusion that's been popping up all over the internet, of the silhouette of a girl spinning in place. The way it's supposed to work, if you watch her for long enough, she'll look like she's spinning in the opposite direction. For me, it never worked. I always, always, always saw her spinning clockwise, and no amount of looking could get her to flip.

Today, I found this animated gif online, and I finally got it. Look at the images to one side or the other to get her to flip directions (or at least appear to). The one in the middle doesn't change. Honest.

http://i.imgur.com/I72qO.gif