The illusion works by only letting you see one in 4 lines at any one time. That means that each fourth line is part of the same drawing as the next fourth line! When the plastic with black lines is moved across your drawing, an animated optical illusion occurs.
There are links below. That’s the images from this video and you can print them out and manage it all by yourself. Please use the transparency mode for the print template and do not change the size of any image, this is very important.
Original link: http://www.youtube.com/watch?v=RBgeKdVHWCs