You will see a rotating wheel that pulsates each time it aligns with two stationary shapes. You may also see that, at the same time, the inner stationary shape wiggles. The pulsations seem to be caused by color assimilation, and the other effects by ambiguous figure-ground segregation.
Read more about the illusion and possible explanations at Peter van der Helm’s website
For another interactive version of this Illusion, see Michael Bach’s “Optical Illusions & Visual Phenomena” website.
Kaleidoscopic motion and velocity illusions Peter A. van der Helm Vision Research, 2007. 47:460–465