Grandmother math always travels with activities to do with the grand kids. In the following video you can see one of the grand sons demonstrate the Woodpecker Illusion.
Both boys made an illusion by cutting and gluing two sheets of paper and then they used crayons to add color to the two patterns that make the illusion. Andrew added apples falling from his tree.
The best use of this simple activity is to stimulate students to create their own two-picture illusion