It was inspired by this video: https://youtu.be/MbXWrmQW-OE
How do you do two different things at once with your arms? How does one arm keep one beat and the other another beat or be hitting something else?
It's the rub-your-head and pat-your-belly thing, only with a bunch of bellies and heads.
The best example is probably Peart's 'drum also waltzes' bit. I can play a lot of Rush tunes and what I can't play still seems learnable with practice.. but that waltz thing he does just seems impossible..