* AlternateCharacterInterpretation: 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.
* AdaptationDisplacement: 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? Although 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.
* AmbiguouslyGay: Many viewers think that Christopher Wren is supposed to be gay, based on his mannerisms and finding Sgt. Trotter to be attractive (as a policeman), "terribly hearty", etc. Officially, he's not.
* ItWasHisSled: Averted. The play traditionally ends with the actors asking audience not to spoil the killer's true identity, so it's not common knowledge despite being "the world's longest running play".
* NamesTheSame: Christopher Wren, the character, shares his name with Christopher Wren, architect of St. Paul's Cathedral. The character is an architect, as well.
* NightmareFuel: Oh very much so and not just at the end. Think about it, you're trapped in a little bed and breakfast inn by a snow storm with people you don't know... and one of them is the killer.
* SpoilAtYourOwnRisk: 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 "TheButlerDidIt!" yelled at their departing backs. Fear not if you are spoiler-averse: there is no butler character in the Mousetrap.
** Even nowadays one could hear the viewers' gasps of shock and amazement during TheReveal in the theatre, so the secret has been kept surprisingly well.