The 1930 novel The Invisible Host by Gwen Bristow and Bruce Manning has a plot that strongly matches that of Christie's later novel, including a recorded voice announcing to the guests that their sins will be visited upon them by death. The Invisible Host was adapted as the 1930 Broadway The Ninth Guest by Owen Davis, which itself was adapted as the 1934 film The Ninth Guest. There is no evidence Christie saw either the play (which had a brief run on Broadway) or the film.
The 1933 K.B.S. Productions Sherlock Holmes film A Study in Scarlet follows a strikingly similar plot; it includes a scene where Holmes is shown a card with the hint: "Six little Indians ....bee stung one and then there were five". In this case, the rhyme refers to "Ten Little Fat Boys". (The film's plot bears no resemblance to Arthur Conan Doyle's original story of the same name.) The author of the movie's screenplay, Robert Florey, "doubted that [Christie] had seen A Study in Scarlet, but he regarded it as a compliment if it had helped inspire her".