One of the Tiki Guards turns to face the catapult.
When the ball rolls around near the Catapult, the Catapult will light up. Now when the ball enters the Catapult, the Tiki Guards will rise up. One of the three will face you and if you hit that one you will receive extra points. You can aim the Catapult by using the flippers to move it left and right. If you are quick you can strike them again before they sink back into the table, but be careful because this can also cause your ball to leave the table.
The Tiki Guards are also used in defeating Big Kong. They rise up to full height, closing the fortress. They must be struck 3 times to lower them one increment and must all be lowered all 3 increments in order for the ball to enter Kong's lair to defeat him. The guards will lower one increment with only one strike from a ball shot out of the Catapult and if you strike two guards from the Catapult at once they will both lower an increment. They also lower an increment if you use the flipper right after the catapult to strike the guards again.