Actors are a superstitious lot. For example, productions of Macbeth have a history of injuries and deaths, so to ward off bad luck, actors usually refer to it as “the Scottish play.” Here are some other theater superstitions.

Leave the Light On

Some theaters are old and dingy places, perfect haunts for ghosts. So it’s become standard practice to have at least one light glowing onstage around the clock, even when the theater is empty. This “ghost light” is meant to ward off bad spirits. Some theater companies use an old floor lamp with a bare bulb (which, in a way, casts exactly the eerie feeling it’s meant to dispel).

Good Dress Rehearsal, Bad Luck

A perfect dress rehearsal is an omen that a play will have a short run. That’s because the cast and crew tend to feel prepared after a good final rehearsal. If they’re too confident, they might lose their nervous edge and goof up. So to avoid a completely perfect final rehearsal, the last line of the play isn’t spoken until the actual performance. If it’s omitted, the rehearsal isn’t “perfect.”

Old Geezers, Good Luck

The “front of the house”—the box office and the lobby—has its own superstitions. One of them is that if the first person to purchase a ticket for a play is an old man or woman, it means the play will have a long, profitable run. But if a young person is the first ticket buyer, the play is doomed to close quickly.

Don’t Whistle Backstage

Theater people believe that whistling backstage brings bad luck to a production. Like most superstitions, there’s no definitive explanation for the origin—it may date back to when sailors were hired to run the rope system that lowered and raised curtains and scenery. Sailors were a good choice, given their skill with knots and manning sails, but they were used to receiving orders via a bosun’s whistle. Thus, the backstage worry: if a sailor heard a whistle, he might lower a heavy curtain or piece of scenery at the wrong time, injuring the actors onstage.