Illusory motion is when an image uses regular shapes and layers them on top of each other to make it look like it is moving. The image isn't moving, your brain just recognizes the shapes and associates it with motion.
If you blink it seems as if it’s moving faster, and if you stare at a certain point it seems to stop moving.
"The Cookie Bite Chronicles." The Cookie Bite Chronicles. N.p., n.d. Web. 18 Mar. 2015.