This illusion is so easy, and so good that you may have trouble believing your own eyes, much less making someone else believe that it is a simple illusion, and not a more complicated trick.

Print out the Koffka Ring Illusion template

Fingerprints are an important part of forensic science, allowing investigators to identify people who have been at a crime scene, or have touched objects. This is a simple way that you can try collecting fingerprints yourself.