An object (e.g. airplane) is turning on a surround (greenhouse), which is swaying back and forth. Observe the rotation of the object. Is it turning smoothly all the time? Or does it “freeze” from time to time? Convince yourself by covering the swaying surround that the object is really turning continuously. If the object is swaying back and forth and the surround is turning continuously we do not perceive a slow-down of the surround. Assuming a stable surround, our visual system probably uses the surround as a reference to measure motion of the included objects.
See an interactive version of the The Freezing Rotation Illusion at Michael Bach’s “Optical Illusions & Visual Phenomena” website
The Freezing Rotation IllusionMax R. DürstelerNature Precedings 2007. 371.1