The theatre profession are a hugely superstitious bunch. Old traditions involve actors never cleaning out their makeup box, and, if they find a thread, winding it around a finger in hope of securing a lengthy contract. Other beliefs are clearly very practical. The embargo on whistling on stage began when stagehands were moonlighting sailors — a mistimed whistle could call a heavy piece of scenery down on your head. The ban on real flowers on stage (they wilt), real jewellery (it plays havoc with lighting design), and having more than two lit candles in a dressing room (your theatre might burn down) are about as superstitious as a health-and-safety manual.
But there is still something here that taps into theatre's natural uncanniness, and the fact that it shares so much of illusion and mystery with the world of superstition. Many theatres keep a cat: these eat mice, which, if unchecked, have a tendency to eat scenery — but they are also witches' familiars. Likewise, the "ghost light", left burning upstage centre whenever the theatre is empty, might prevent someone from tripping over in the dark and breaking their leg, but also appeases theatre ghosts by allowing them to stage their own performances one night a week.
It is not surprising that the play around which most theatre superstitions circulate is Macbeth. One rumour says the play's three witches cast real spells, and Jacobean necromancers cursed the play as a punishment to Shakespeare.
It is the web of such rumours that have made the world of theatre superstition
Perhaps on Halloween, when the veil that separates the worlds is especially thin, we might do well to obey the superstitions that adhere to that thinnest of veils: the stage curtain.