Never say 'Macbeth'
According to a theatrical superstition called the Scottish curse, speaking the name Macbeth before a performance will cause tragedy - as a result the lead character is often referred to as the Scottish King. Those who believe in the curse claim that real spells are cast in the three witches scene.
Productions of Macbeth are said to have been plagued with accidents, many ending in death. The legend of the curse dates back to the premiere of the play when an actor died because a real dagger was mistakenly used instead of the prop.