There are four slots above the flippers. Each of these has a slot machine wheel above it. When you enter the slot below that wheel, the wheel will spin. If all four wheels match, you will receive whatever they show:
Ball Saver - The post between the flippers will pop up, making it less likely that you will lose the ball between the flippers.
Multiball - An extra ball is added to the board.
Trapped - A shield is thrown up around the Labyrinth area that keeps the ball trapped. However the Ball Saver is also activated, making it easier to keep the ball in play. The ball can still escape through the slots. Also if you light up all the spinners in the trap you will escape and receive a bonus.