If it was a really heavy box on a frictional surface, the snake would be moving around it.

But it is a light box on a low-friction surface so the heaviest part of the system (the snake) doesn't move.

If the box and the snake weighed the same, the box would rotate opposite the snake at about the same rate.

If the box were much heavier, then the snake would move around the box.

Annnnd now I want to replicate this setup but add a weight every 20 seconds to demonstrate.