If you look above you, you will see the Klystron Generator. On it is marked "KLSTRON GENERATOR. DANGER, DO NOT REVERSE POLARITY." Polarity reversal is a very dangerous procedure, that's why we tell you not to do it. However, in the unlikely event of entering a polarity reversal situation, we ask you to follow this simple drill.
STEP ONE: Put your hands in the air.
STEP TWO: Place your hands on the cranium.
STEP THREE: Press in a downward motion.
STEP FOUR: On the command 'Polarity Reverses', equalise your external equilibrium by exhaling thus - phew!
Music is "SHAKE, RATTLE AND ROLL"