Although the movie takes place in 1957, at least four recordings played on the phonograph post-date that year: "Shakin' All Over," "You've Been Talkin' 'Bout Me, Baby," "Kookie, Kookie, Lend Me Your Comb" and "Alone At Last."
At 01:35:09 the police place a ceramic mug into a plastic bag as evidence. However in 1957 a Police Evidence Bags were all made of paper, therefore a Police Evidence Tamper Proof Security Envelope should have been used.
In the extras, Simon Bowles asserts that Crooked House (1949) is the last novel written before Christie's death that didn't employ Miss Marple or Poirot. In fact, the following 10 novels were published after Crooked House without Marple or Poirot:
They Came to Baghdad (1951)
A Daughter's a Daughter (1952 as Mary Westmacott)
Destination Unknown (1954 aka "So Many Steps to Death")
The Burden (1956 as Mary Westmacott)
By the Pricking of My Thumbs (1958)
Ordeal by Innocence (1958) and The Pale Horse (1961) although Marple is artificially placed in these itv adaptations she does not appear in the original works)
Endless Night (1967)
Passenger to Frankfurt (1970)
Postern of Fate (1973)
Charles gave the car repairman a starter cable, which he had obviously removed himself, and claimed this is the reason the car would not start, however, when he tried to start it, the starter worked perfectly, but the engine would not fire. This implies that it was the ignition system that he tampered with, not the starter motor.
Although the movie takes place in late 1957, Charles Hayward (Max Irons) goes to the local cinema, sits down and is seen watching a newsreel. Incorrectly all of the cinema's house lights are switched on at 100% light output. During the projection of all of the advertising slides, the cinema's house lights are always switched on at 100% light output. However when projecting motion picture films i.e. whilst screening the newsreel and the feature film(s), the cinema's house lights are always switched completely off.
The goof item below may give away important plot points.
A car plunging down into a quarry will not explode when it hits the bottom. Contrary to popular belief, liquid fuel is not explosive, it isn't even flammable. What explodes is vaporized fuel - and then, only if mixed with air in a precise ratio. A small fire was just possible, but it's the big impact which is deadly.