The Paranormal Piano Player

The other evening I was watching a Yamaha player piano performing by itself in a hotel foyer. For anyone unfamiliar with these marvels, a player piano is an automated real piano with a mechanism to work the keys and pedals. Watching it play happily to itself, it's quite easy to imagine an invisible pianist on the ivories, giving it big licks. Quite easy, but what makes the illusion not wholly