And why you get that occasional creepy feeling . . . but hey, it's science.
A report from the U.S. Department of Transportation confirmed Thursday that at any one time, the average American city bus is occupied by at least four fully erect penises. "This persistent level of physical arousal remains a mystery, as we have found no link between these erections and either the attractiveness of fellow passengers or the intensity of vehicle vibrations," the report read in part, also noting that when one of the four engorged penises goes flaccid, another immediately hardens, as if to take its place.