I love optical illusions and visual novelty of all kinds. This illusion of a rotating ballerina kept me busy for a while. The direction which you first perceive the dancer to be spinning supposedly reflects your dominant brain hemisphere.
However, I've confirmed that you can also change the apparent direction. I did this by flicking my eyes away for an instant, by clicking the animation for a moment to freeze it, and by scrolling until only the legs the dancer was shown. The rest is up to your mind changing its perception.
I found this to be as thought-provoking as the Magic Eye images. Something that you are looking at instantly and completely changes form, direction, or context due to nothing other than a change in the perception of the individual. Click below to see the illusion: