Yar appearance:
Take the Chai and an optional parachute to the flying saucer mesa area. Walk off the mesa and drop the Chai when Indy starts to fall. Yar, from the game Yar's Revenge, will appear at the top of the screen.

Programmer credit:
Enable the "Yar appearance" code. Then continue game play and obtain a high score. "HSW2", the initials of programmer Howard Scott Warshaw, will appear in the inventory after the game has been completed. Note: The "2" indicates that this was his second game.