This movie was made and released about forty-one years after Agatha Christie's source novel of the same name was first published in 1941. This picture was the first ever filmed version of this story, it being remade with Agatha Christie: Poirot: Evil Under the Sun (2001).
The game that Odell Gardener is playing when Poirot asks him about his whereabouts during the murder is pétanque, a French game in which players have to throw hollow metal balls as closely as possible to a wooden one.
Second of six appearances playing Detective Hercule Poirot by Peter Ustinov. Ustinov played Poirot here between playing him in the movies Death on the Nile (1978) and Thirteen at Dinner (1985).
Poirot claims that Daphne could not possibly have seen in the mirror Kenneth Marshall sitting at the desk typing. However, the next shot is of the desk from Daphne's viewpoint and the typewriter is clearly visible. If Kenneth had been typing, his hands on the keys would be in view, and if he were leaning forward, a large part of his body would be as well.
When Poirot performs the magic trick for Linda Marshall, she replies "I know how you did that. The egg's in your top pocket." However, Poirot's top pocket is flat and cannot contain the egg.
Daphne Castle: Arlena and I were in the chorus of a show together, not that I could ever compete. Even in those days, she could always throw her legs up in the air higher than any of us... and wider.