The typical form which the allegory takes is that of a series of pictures, sculptured or painted, in which Death appears, either as a dancing skeleton or as a shrunken corpse wrapped in grave-clothes to persons representing every age and condition of life, and leads them all in a dance to the grave. ["Encyclopaedia Britannica," 11th ed., 1911]
It is strange how the effect of this music has exerted such a long surviving influence on members of the dramatic profession. It is still considered most unlucky to sing, hum, or whistle the witch airs in the theatre except in the ways of business. [Young-Stewart, "The Three Witches," in "The Shakespearean," Sept. 15, 1896]
If you number an actor or actress among your friends, and desire to retain his or her friendship, there are three things you positively must not do, especially if the actor is of the old school. Do not whistle in the theatre, do not look over his shoulder into the glass while he is making up, and do not hum the witch's song from "Macbeth." ... [O]lder actors would almost prefer to lose their salary than go on in "Macbeth" on account of this song. They believe that it casts spells upon the members of the company. ["Some Odd Superstitions of the Stage," "Theatre" magazine, July 1909]