Thaumatropes

Persistence of vision is the theory that the eye registers an after-image of any moving object for approximately 0.04 seconds; this would mean that everything we see is a mix of what we are seeing and what we have just seen. This optical illusion was used to good effect with the invention of the Thaumatrope; this was a toy that had an image on the front and an image on the back that, when spinning gives the illusion of one more complex image.