"When a theater goes dark for the night, a stagehand leaves a lighted lamp on stage. No one knows why any more, but some old timers say it is to keep the ghosts away. Others say it lights the stage for the ghosts to play. Whichever theory one adheres to, most people agree: a great theater is haunted."

Source: Emily Post (2007). “Etiquette: In Society, in Business, in Politics and at Home”, p.58, Cosimo, Inc.