Anybody who's ever watched a car commercial recognizes the sight: a hot new model whizzing along while its wheels appear to spin in reverse. Not particularly noticable on cars with solid wheels, it's often shuffled into stark relief when a spinning spoked rim gets out of phase with the frame rate of the camera. A frame captures one spoke, while the next frame captures the upcoming spoke in a slightly different position during deceleration, inducing the illusion of backwardness. It's all explained at the link below, which also offers up multiple theories for the "Freebird"-yelling phenomenon, which may or may not have to do with Florence Henderson.
Glad You Asked: Why do wheels on cars in commercials appear to go backward? [Racine Journal-Times]
New York City for Dummies: How to Ride the Bus [Internal]