There is a Bride of Frankenstein connection to this motion picture, both Elsa Lanchester and Una O'Connor costarred in that monster classic.
This was Una O'Connor's last big screen motion picture.
This was the final film for Tyrone Power, who died shortly after completion.
To perfect her disguise as the "Cockney Woman", director Billy Wilder did a series of screen tests of Marlene Dietrich. The first attempt almost ended the idea when, after making up Dietrich in wigs, contact lenses, false eyelashes, false teeth and shoulder pads, Wilder commented that she looked less like a Cockney woman on screen and more like "George C. Scott in drag".
Unsure if he could play a man with a heart condition, Charles Laughton (Sir Wilfrid) staged a heart attack in the pool one day at home. His wife, Elsa Lanchester (Miss Plimsoll), and a houseguest panicked and pulled him from the water, at which point he explained his trick. Elsa's reaction has not been recorded.
When Leonard Vole (Tyrone Power) meets Mrs. French (Norma Varden) for the second time - in the movie theater - Vole tells Mrs. French that the movie is about Jesse James. Tyrone Power starred as the famous outlaw in Jesse James.
While it is generally supposed that Agatha Christie chose the name Vole after the ratlike rodent of the same name, in fact the word has several other meanings also relevant to this character. In cards, a "vole" means the winning by one player of all the tricks of a game. And the expression "go the vole" can mean either to venture everything on the chance of great rewards, or to try one thing after another, usually a variety of occupations - all perfect descriptions of Christie's ingeniously named "Leonard Vole".