Do you see two or three elegant women? Illusions that generally feature two figures whose contours match seamlessly the contours of another figure inducing the viewer with a mental choice of two interpretations, each of which is valid, are related to Rubin’s vase illusion, named after the Danish psychologist Edgar Rubin who introduced this illusion in his work 'Synsoplevede Figurer' ("Visual Figures") published around 1915.
This optical illusion has been created in three dimensions. It is a real object. However impossible things seem to happen! The wooden balls seem to roll uphill. It cannot be magnets - they do not work on wood! This wonderful illusion was created by Koukichi Sugihara from the Meiji Institute for Advanced Study of Mathematical Sciences in Japan. In May 2010 this video was the winner of the Best Visual Illusion of the Year Contest 2010.
However once the structure rotates, we can see that it is not constructed as we initially thought. We might have thought that the wooden balls were rolling uphill. Once we view it from the other side, we can see that in fact the balls are rolling downhill, and that the laws of physics are still being obeyed.