I was looking for something to create an optical illusion for a group of Webelos Cub Scouts, while we worked on the Webelos Scientist Activity Badge. On achievement #12 it says: "Show in three different ways how your eyes work together, and show what is meant by an optical illusion." All I needed was an optical illusion that the boys could create themselves, to give them an idea of what an optical illusion was, then have them create one and explain how it worked. I came across this idea here: http://www.cometogetherkids.com/2012/03/optical-illusion-handprint.html. I did it myself and it was fun to do and a really great finished product. I did it with the Webelos Cub Scouts and they loved it too. Be aware that this is a time consuming project, but if you have kids recovering from an illness, or stuck inside on a rainy day, or need a Plan-B to fill time, this might be just the project to keep them busy. So here is how to draw a 3-D Hand Print.
White paper (make it just larger than the hand being drawn, this is a 8.5x11 inch piece of paper cut in half)
Piece of scrap paper (not shown)
Colored markers (wider tipped markers work best)
Choosing what order you want to put the colors, start drawing across the width of the paper. Have the next color right on top of the color before it. When you finally reach the pencil line of the drawing of the hand, curve the line a little upward in a gentle arc, ending on the other side of the hand line at the same level as you started. Keep adding the curve each time you come to a hand print line.