Circles Within Circles Optical Illusion The image here appears as if it's pulsing to us. Look really hard and you can see the black and white colors in the image that work to make it look as if it's moving.
Neuroscientists figure out how this snake illusion works. Right before the snakes start to move, you begin blinking more and making short jumpy eye movements called microsaccades. See: April 25 Journal of Neuroscience.