Is there a real Macbeth curse?

Some actors believe it's bad luck to say 'Macbeth' in the theater unless the play is being performed -- but why? In this episode, Katie and Sarah explore the origins of the Macbeth curse and the life of the historical Macbeth. (And, an important note: The error regarding "Our American Cousin" and Abraham Lincoln has already been corrected in the episode He Was Killed By Mesmerism.)