The rarest event I have witnessed while playing was a dealer spins the ball and the ball flies out of the wheel and across the room. The dealer then takes the spare ball from the centre turret and spins again. This time the balls flies out of the wheel, up in the air, comes down and ricochets around the wheel a bit, then files up in the air again and plonks back into the centre turret. So the spare ball lands back exactly where the dealer took if from. A truly incredibly rare event.