Smelly Cat Smelly Cat, Where have you been ?
These are the poetic, laughter evoking lines sung by Phoebe&friends in one of the Friends episodes.
It would sound like a prose recital and when she asks for friends to join in, it becomes 'n' times fun
Actually come to think of it, the melody behind those lines are def hummable....
Disclaimer: If you dont really find any reason, why this is funny please watch TBS - they have been running promotion of 'Its funny on TBS' with this scene often, that should fix your problem. If it still does not fix it... forget it.