I have no idea why they started doing this, where it came from, or what prompted it, but they did it frequently throughout the Christmas season. They also did it once last week around the coffee table in the front room.
Two other notes:
1. I love that Joey's always in the middle of it all with some random toy in his hand, being knocked to and fro, and perfectly content.
2. Joe's ability to sit in a room completely undisturbed and unaware of the small children running about, making large volumes of noise, seems to be hereditary.