Do you see gray areas in between the squares?
If you take a look at the following picture , let me tell you ... it is not 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 aft er you take your eyes away from it.... Weird