Continuity mistake: Widmark's eyes are open when his body is discovered. But in the scene he is drugged he is last shown with them closed.
Factual error: The Locomotive pushing the snowplow close to the end of the movie is a French 141 R. They entered service from 1945 on, ten years after the movie is set.
Visible crew/equipment: When Ratchets gets up from the dining room table after Poirot turns him down, you can see the cameraman in the silver buffet on the table.
Other mistake: In the original version of the film there's a mistake in the opening credits where Colin Blakely's name is misspelled as Colin Blankey.
Factual error: In Istanbul we hear the standard Arabic-language call to prayer (beginning "Allahu Akbar!"), but the film is set during the 1930s when Kemal Atatürk was in power and muezzins were required to use a Turkish-language call to prayer (beginning "Tanrı Uludur!") instead.
Other mistake: The opening montage shows the news story of the kidnapping of the Armstrong child unfold through newspaper articles. The kidnapping takes place in April 1930, but next to the headline of The Police Gazette about the getaway car, you can read a headline (incidentally, from a magazine with the name of the victim in place of the publication's name) that says "Snow-covered Rocky Mountain states feel first winter blasts." First winter blasts, in April. (00:03:45)
Chosen answer: They planted this red herring not to divert Poirot's attention away from them - they were the only passengers on the train - they wanted to divert him from the fact that they were ALL involved in the murder, because they all had a common bond with the child whom the victim murdered. Each one made out like they didn't really know anyone else on the train, but they were all in on it.
Kimberly Klaus