I read a description (long ago) in one of the Opies' books.
They were watching some children play near a muddy puddle. From something that happened the children evolved a rhyme, and all ended up chanting -
its a duck
Stuck in the muck.
The Opies went away thinking they'd seen the creation of a new peice of childlore, but when they saw those children again it had been forgotten.

What has that got to do with anything?
Nothing. Except perhaps, that playing with words is a natural habit.