If an actors whistles during rehearsals or in their dressingrooms during a play it is believed that the play will be doomed to failure and presumably the whistler will soon be out of work..

According to Kevin Robertson's Dissertation on Theatre Superstitions, "The reason for this superstition is as follows: before the advent of walkie-talkies or clear-coms, cues for theatre technicians were called with a sailors whistle. Therefore, one who whistles in a theatre may, inadvertantly, call a cue before it's time, setting all types of catastrophy into motion."