Illusions process in the brain. They change your perception of reality making you think that what is true is false, and what is false is true. Most of the time, your eyes, body, and head are in motion. This makes it hard to detect an object in motion with a image in motion. In a movie, we believe that the objects are moving, but they are just pictures that have been placed in such a fast motion that the object seems to be moving. Your brain interprets things that are not possible.