Theater Superstition - Bad Luck to Whistle

Superstition: It is considered bad luck to whistle on or off stage, as someone (not always the whistler) will be fired.

The reason for this superstition was that before the invention of walkie-talkies or comms, the cues for the theater technicians were coded whistles given by the stage manager. If one was whistling backstage it could call a cue before its due, which could have disastrous outcomes resulting in someone losing their job whether it be the whistler, the stage manager or the technician.