M*A*S*H (1972)

S6E14 The Merchant of Korea

When Charles gives B.J. two hundred dollars, B.J. starts to exploit the situation. The group convinces Charles to join a poker game, where he astonishingly wins with sheer beginner's luck. However, Radar notices that Charles whistles loudly whenever he’s bluffing. Armed with this knowledge, the gang manages to reclaim their money and even profit from the game.