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My guess: a flywheel inside the ball to keep it stabilized, along with a motor and series of magnets to move the "head" around.

Sure, but how exactly? If I hadn't seen the video I would have guessed a practical prop impossible.

Mashable has an article about it, but they too have some hand-wavy-magnet explanation.

Too bad there is no discussion on hn or reddit about the workings.