Excellent Optical Illusion

My son introduced me to these impressive, inverted-face optical illusions from Grand Illusions. They come in the form of free PDF files. Download, print, cut and fold. If you're interested in such things or you want to amaze your kids, the exercise is definitely worth the effort. There's a demonstration video on the page as well.

link

p.s. Check out the site. They sell a number of really cool gizmos and illusions.