The silhouette seems to be rotating clockwise, but if you concentrate you can make it reverse, and seem to be going counter-clockwise. Until you see it switch you'd think it's impossible.
I suppose the reason is that you are constructing a three-D model from a 2-D image, and either model is compatible with the image, but each is completely different. It's very strange.
The way I made the image switch was to look at the text below the picture, from which angle it's impossible to construct the 3-D model. Seen like that the swinging leg looks like a pendulum, going back and forwards not round and round, and it's possible to choose which model you want to use.