Multiball has just been awarded by lighting the three lights shown.
Light up the three dropdown targets at the upper right of the board to start multi-ball. The game considers the extra balls to be paratrooper reinforcements that come flying in. A few seconds after the multi-ball starts, the right passageway will light up (see below). The red squares will light up showing your progress. When you light all three, you are awarded a bonus. If you pass through here three times, you will get a "perfect landing" bonus for saving all of the paratroopers.
After multiball starts red lights of the right passage start blinking.