Thaumatrope

The Thaumatrope is an optical allusion toy, invented in the victorian times by either John Ayrton Paris or Peter Mark Roget. Both inventors often get credited for its creation.

It is usually made from a circular piece of card that has an image on each side, for example a bird on one side and a cage on the other. It has string at each side of the card that is twisted to allow the card to spin around quickly, and when spun displays the whole image, creating the illusion of the bird now being in its cage.

The reason we see both images in one is because of 'persistence of vision'. Persistance of vision in simple terms is the delay between what we see entering the eye and reaching the brain, leaving use to see both images at once and leaving a kind of indent of the previous image on the brain before the second one reaches a loving them to 'blur' or 'much' together.