Eye movements cause the illusion to appear. Your eyes dart around even when you stare at a static object. Normally, your brain can distinguish between the movement of your eyes and the movement of an object. However, your brain is puzzled by the illusion’s dramatic contrasts and shapes. The image appears to turn as your motion sensors activate.
Because movement can be an indication of danger, your brain developed to focus attention on it. However, the movement you observe in this image is an optical illusion manufactured in your mind!