Unbet

[…] after you have tasted the sweets of victory, you will begin to share my view that it is fun just to sit and watch a race on which you have not bet. It is fun even when the unbet race is won by a horse you rejected at the paddock.

A temporary $500 bet is made on one horse, chosen at random by flipping a coin, and movements in betting on that horse and on the unbet (control) horse were recorded.