Take a look at this picture. It isn't animated! Your eyes are making it move. To test this, stare at one spot for a couple seconds and everything will stop moving. Or look at the black center of each circle and it will stop moving. But move your eyes to the next black center and the previous will move after you take your eyes away from it.
(when prof scouts for next person to recite, i stop moving. hehehe.)
they say, the faster it moves the more stressed you are.