- Adaptation Displacement: To some degree, anyhow. Think about it: how often do you hear anyone refer to the original short story or radio play Three Blind Mice instead of the play? However, that's partially due to publishing of the short story being banned in its home country until the show stops running. It was, however, released in the United States.
- Alternate Character Interpretation: Mr. Paravicini sometimes gets this in various productions. Most portray him as a stereotypical Italian who talks-a like-a this and such. Others, however, portray him more like an Italian mobster, giving him an edge of sorts.
- Nightmare Fuel: Oh, so very much - and not just at the end. Think about it: you're trapped in a little bed and breakfast inn by a snowstorm with people you don't know... and one of them is the killer.
- Spoil at Your Own Risk: The twist ending that they implore you to keep secret. Most productions of the play even bill themselves as "the longest-running secret in the history of theatre!", or variations to that effect. Most people actually obey. A joke among theatre insiders tells of an American couple going to see The Mousetrap, tipping their cabbie poorly, and having "The Butler Did It!" yelled at their departing backs. Fear not if you are spoiler-averse: there is no butler character in The Mousetrap. Even nowadays one can hear the viewers' gasps of shock and amazement during The Reveal in the theatre, so the secret has been kept surprisingly well.
YMMV / The Mousetrap