The fictitious country where most of the story takes place is named in the movie: in her first scene, Miss Froy says, "Bandrika is one of Europe's few undiscovered corners." The first two stations in the movie are identified by briefly visible signs, and the third in dialog: they are Zolnay, Dravka, and Morsken.
In an interview with Peter Bogdanovich, Alfred Hitchcock revealed that this film was inspired by a legend of an Englishwoman who went with her daughter to the Palace Hotel in Paris in the 1880s, at the time of the Great Exposition. The woman was taken sick and they sent the girl across Paris to get some medicine in a horse-vehicle, so it took about four hours. When she came back she asked, "How's my mother?" "What mother?" "My mother. She's here, she's in her room. Room 22." They go up there. Different room, different wallpaper, everything. And the payoff of the whole story is, so the legend goes, that the woman had bubonic plague and they dared not let anybody know she died, otherwise all of Paris would have emptied.
In the original cut, as seen in the 25th Anniversary national re-release of 1963, Charters and Caldicott have to share the same pair of pyjamas in the hotel after Charters has accidentally dropped his in the water jug. In later years and showings this innocent preamble has been snipped out and there is a cut straight to them in bed together. Though we can still see Charters' pyjamas hanging up to dry, the explanation has disappeared.
The cricket match that is being talked about in the movie by Charters (Basil Radford) is the description of the actual third Ashes test between England and Australia at Manchester in 1938. The result of the test match quite rightly was shown in the end through a newspaper headline - "Match abandoned due to rain".
Although he uses the fictitious Bandrikan language when speaking to his staff, at the end of the phone conversation in which he conveys Iris' room service order for "champagne", Boris, the harassed hotel manager, exclaims, "Oy vey is mir", a Yiddish expression meaning "woe is me."
Leslie Gilliat shot screen tests, including that of Michael Redgrave (with and without moustache), and later remembered that when testing one actress for the role of Miss Froy, Alfred Hitchcock instructed him not to put any film in the camera, since he had already secretly and successfully negotiated for May Whitty to play the part.
Whilst in the baggage car, Gilbert and Iris playfully acting along as Sherlock Holmes and Watson, Gilbert offers a Trichinopoly cigar (although the prop itself is a fountain pen) to Iris as a sort of prize in an earlier observation. A Trichinopoly cigar was an important clue in Sir Arthur Conan Doyle's "A Study in Scarlet", the first Sherlock Holmes story.
Gilbert says he once drove "a miniature engine on the Dymchurch line". The Romney, Hythe and Dymchurch Railway is a real-life miniature (1/3 normal size) railway in southeast England, which in 2003 still uses steam locomotives and carries passengers over 13 miles of route.
The failure of the original copyright holder to renew the film's copyright resulted in it falling into public domain, meaning that virtually anyone could duplicate and sell a VHS/DVD copy of the film. Therefore, many of the versions of this film available on the market are either severely (and usually badly) edited and/or of extremely poor quality, having been duplicated from second- or third-generation (or more) copies of the film.
The International Herald Tribune that Charters and Caldicott read to look for the cricket score has a headline on the back page referring to Temple's 60-36 victory in the championship game of the first basketball National Invitational Tournament, played on 16 March 1938.
The earliest documented telecast of this film occurred Monday 18 December 1944 on New York City's pioneer television station WNBT (Channel 1). In Los Angeles, post-WWII television viewers got their first look at it Saturday 2 July 1949 on KTSL (Channel 5).
The plot has clear references to the political situation leading up to World War II. The British characters, originally trying their hardest to keep out of the conflict, end up working together to fight off the jack-booted foreigners, while the lawyer who wishes to negotiate with the attackers by waving a white flag gets his just deserts.
Actor Michael Redgrave actually went to Cambridge, just like his character, Gilbert. He was also a chorister and took singing lessons early on in his career which gives more credibility to Gilbert's statement that he has "a powerful voice".
Many of the film's themes occur in the thriller Flightplan (2005) with Jodie Foster, such as someone vanishing from a moving vehicle, a dizzy woman as only witness, writing on the window as proof, etc.
The trivia items below may give away important plot points.
A musician is mysteriously strangled by disembodied hands after serenading Miss Froy under her hotel window. This is not one of the film's loose ends as previously reported. Froy uses a musical code and the singer can be assumed to be passing information to Froy. Note that Froy is carefully listening to the notes, not just enjoying the serenade. The singer is an informant or another spy.
In order to get a realistic effect, Alfred Hitchcock insisted that there should be no background music except at the beginning and the end of the film. Between those two points, the only music heard is the music sung by the musician outside the hotel, the music tune of Miss Froy, the "Colonel Bogey March" music hummed by Gilbert (Michael Redgrave), the dance music conducted by Gilbert in his hotel room and the dance music when Iris (Margaret Lockwood) meets Gilbert in the train.