- Development Hell: The film rights for the play have been bought and sold over the years, but always with the proviso that production not start until the play has been closed in London for six months, which only finally happened in 2020 because of the COVID-19 Pandemic. Even then, the show returned the following year, so no, COVID-19 is not going to provide whoever currently owns the film adaptation rights an excuse to start making one right away.
- It Will Never Catch On: Christie herself thought it might last about eight months in the West End. Six decades later...
- Name's the Same: Christopher Wren, the character, shares his name with Christopher Wren, architect of St. Paul's Cathedral. The character is an architect, as well. Deliberately invoked In-Universe, as this is just a pseudonym.
- No Adaptations Allowed: None can be made while the play is still running.
- Unintentional Period Piece: In 1952 this was a contemporary play. A mention of ration books meant this was already showing its age just two years later when rationing was abolished. The radio being the source of news and entertainment, the fashions (possibly much more overtly "1950's" than they would have been in the actual 1950's), and especially the shock of a woman wearing trousers cement this firmly in a narrow time period.
Trivia / The Mousetrap