After some trial and error, and even though he's still unclear on the concept, Parker finally got down and dirty with the tug toy yesterday:
Did I mention the "trial and error?"
He did, eventually, put all four paws into it:
He also killed one of his oldest toys last night, the lion-head tennis ball he's had since he couldn't even get down the stairs by himself. Yeah, once he started working on it, he spent less than five minutes scattering stuffing all over the floor. So now he has a tennis ball that used to have a lion head on it.