How does it work? Someone suggested the following answer:
I’d expect that the inertia of the swing arm movements is causing the plinth to roll slightly so that when they get to the end of their swing it gives them an extra split second of balance (like the zenith of an object that’s been thrown in the air). The other arms (in the middle of their swing) then have time to catch up. As more of them sync up, the plinth moves more, as in a feedback system.
Spotted on B3ta.com.