Which Way Did the Bicycle Go?
A bicycle leaves a pair of tracks in a mud patch with its front and rear tires. Because the track colors and direction in which the bicycle is traveling get shuffled with every track generation, this Demonstration can serve as a puzzle. Deselect the "show solution" icon and click the button "retrack." Now try to determine the traveling direction and the track of the rear tire. Then verify your answer by pushing the bicycle with the slider or click Play to let it drive itself. Adjust traveling speed.
 J. D. E. Konhauser, D. Velleman and S. Wagon, Which Way Did the Bicycle Go?: And Other Intriguing Mathematical Mysteries, Washington, DC: The Mathematical Association of America, 1996.