Entry in progress—BP
   
Toby Simkin
Theatre Superstition
The Last Line
It has been considered bad luck to say the final line of a show before it opens. Therefore, many rehearsals skip the final line of the play, or invite a few family, friends, and reviewers to see the dress rehearsals.
 
3 March 1882, The State (London, UK), “Stage Superstitions,” pg. 8, col. 2:
Let us see what some of our particular superstitions are:—It is superstitiously unlucky to sing the lovely strains of Lock’s music to Macbeth or the National Anthem except at rehearsal or performance. It is ditto to speak the last line of a tag at rehearsal; to whistle in a dressing-room, unless every one in the room immediately whistles too, &c., &c., &c.
   
News & Record (Greensboro, NC)
WHAT LIES BEHIND CURTAIN? SUPERSTITIONS
BY LESLIE MIZELL Special to the News & Record Dec 11, 2002 Updated Jan 26, 2015
(...)
Rehearsals: Supposedly, a bad dress rehearsal indicates a good opening night. This superstition has fairly obvious origins in a director or producer trying to boost morale and quell anxious nerves in his actors before a performance. Likewise, some think it’s bad luck ever to say a play’s final lines in rehearsal: Its first time in its entirety should be in front of an audience.