"We rode the F train and L train for about 4 hours one Sunday documenting the actual way bottles roll around on a subway car. We didn't contrive any of their motion. We just tried to anticipate where they might roll or be kicked around and let them do their thing on the way to and from Canarsie and then Coney Island."

From http://www.boingboing.net/2008/01/08/video-of-bottles-rol.html ...