Show an opaque plastic case. Open the lid to show the inside. The inside looks like a cutaway view of a funnel. Drop a Quarter into the top of the funnel. When it comes out the bottom, it has changed into a little tiny coin. Do this three times. Each time a shrunken coin drops out the bottom. Now, turn the case over and drop two of the tiny quarters inside. Suddenly, they change into a full-sized Half Dollar.