From Gary's YouTube description
Inspired by *The Invention of Hugo Cabret*, I built this automaton from scratch, using information I found around the Internet. The dog moves his head and tail while a ball bounces next to him. Though simple, the mechanism uses a cam, a crank, a crank slider and linkages. It was the most difficult craft projects I've ever attempted, and the result hardly shows it. But it was a fascinating endeavor.