This animation is an optical illusion, made of 34 frames. Depending on the perception or frame of mind of the viewer, the dancer will spin either in anti-clockwise or clockwise direction, and some people are also able to make her change direction at will. If you cannot do it, go here – before you loose your mind. This animation has been blogged and commented upon widely, it seems to make peoples’ heads spin too. Most reports state that whether you see her turning clockwise or anticlockwise indicates a right or left brain dominace, however this is contested in the New Scientist. The image simply does not provide enough information for the brain, so it just fills in the rest, as with other optical illusions. However, they dont give an answer to why many people seem to have difficulties seeing it one way or the other. As John McCrone states here in this overview of research about brain lateralisation, very little about the brain is ever straightforward.