It basically works by making your mind try and figure out what direction the image appears to rotate, which the animation appears to confuse by using the two-colour scheme that does not allow for the determination of the direction of rotation as there are no clues available through gradient shading. So, the mind takes over and “fills” in the details on what one should perceive as the direction of rotation.
With some practice, I could make the tail “rotate” clockwise, while the body went the other way, LOL!
The key is to try and choose what you “want” to be in the foreground.
Cool - I tried - but can't do that one...