To make a Thaumatrope.
To make a thaumatrope can be made as follows. Use a scissor to cut out a square piece of cardboard, each side of which measures about 3 inches (9 cm). Then pierce a hole near each of two opposite edges. Then attach short pieces of thick string as shown in the diagram. Draw a fish on one side of the cardboard and on the other side a bowl.
Then hold the string between the thumb and first finger of your hands. Twirl the cardboard square rapidly by sliding the thumbs over the fingers. A composite picture of the fish inside the bowl is seen. The reason for this is that the thaumatrope demonstrates the principle of "retinal retention", which is the ability of the eye's retina to retain an image for a fraction of a second after the object disappears.