(laughter)
When I first saw this thread, I thought you meant the kids' television show called Wishbone. It starred a small dog with a vivid imagination. He starred in a variety of roles in literary classics, with narration from Wishbone of the story and his actions. Imagine a Jack Russell terrier playing Mr. Darcy and you get the idea.
I was told by a folklore professor (mind you, she was several sandwiches short of a picnic, so take this with a huge grain of salt and some extra on the side) that the tradition had to do with breaking physical objects to release energy.