This apparently is a well know short video of a dancer twirling on her foot. The question is whether she is going clockwise or counterclockwise—or whether you can see her going in either direction if you think about it. It's useful to blick or look away to make her switch direction.

Initially I see her going to her right. If I click the stop/play button to stop and start the video, she often changes direction. Since she always moves in the direction of her outstretched arm, the arm changes from being her right arm to her left arm!