I love this little illusion! I use the quarter size chinese coins with square holes instead of quarters and I printed a small spiral from the internet that I taped on the disk in the middle of the illusion (with double sided tape). When you turn it, it looks like you are travelling through a vortex. Using the chinese coins with a square hole opens the door to a lot of fun with "square holes penetrating round holes" and talk about creating your own personal vortex. It is fun for kids and adults. Personally, I have a few of these. I keep one on my office desk, one at home, and one wrapped in a piece of chinese newspaper that I can drop in my pocket.