Well as you know butchers traditionaly deliver whole sides of meat hanging from rails in their trucks. There was one such truck that was having trouble driving up this hill. It would get a little bit up the hill, then would not be able to continue and would jerk back to the bottom again.

A passer-bye suggested to the driver that his truck was overloaded. The driver responded replied that it was well under its wieght limit. Saying it's not the meat it's the motion.

That passer-bye was Henry Grover who later mentioned the incident to Lois Mann and the song was born...........

Honest.