[bucklebone]

There's a history of pop songs or nursery rhymes or kids songs that have morbid overtones. Just recite "Rock a Bye Baby" to realize how morbid that is: "...and down will come baby, cradle and all." Or, "Ring Around the Rosie" when you learn that Posies are the flower of choice to place on the casket of a loved one.

Or "Bungalow Bill" Hey, Bungalow Bill, What Did you Kill...

I think its a joke that the writer is playing on the listener. Let's see what morbid words I can get my listener to sing while humming this happy tune.