The play's ending is different from the movie's on a couple of points.
When Mortimer learns he is not a Brewster relation whatsoever but an illegitimate child taken in by them out of pity; in the play he tells Elaine, "I'm a bastard!" with great (and comical) joy. In the movie, the line is changed to "I'm not a Brewster! I'm the son of a sea cook!" since the Production Code which governed movie production during this period forbade strong language on the screen (Gone with the Wind's "Frankly my dear, I don't give a damn" aside).
In the play, Mortimer's aunts remain out of an asylum. They learn the owner of Happy Dale is a lonely person, and the curtain falls as they offer him one of their infamous glasses of elderberry wine, implying they will continue to mercy-kill people. In the movie, once again due to the Production Code which would not allow criminals to remain unpunished for their crimes, the aunts are sent away to the asylum and the owner is spared when Mortimer intervenes.
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