Continuity mistake: The cream colored shoes of the Lady are prominently featured in the finale. When the actress has to run, not only are the heels replaced by modern tennis shoes, but they're black, in contrast with her white stockings. (00:46:40)
Other mistake: The closing credits on the DVD are for another episode, "The Kidnapped Prime Minister." (00:47:15)
Plot hole: When Poirot and Hastings break into the house, they search the entire house for the box, without success. However, later on, when they are in the kitchen, the housekeeper comes down the stairs - having been lying in wait for them. How did Poirot not run into her when he was initially searching upstairs, particularly when he was making such a thorough search?
Factual error: The episode is set at a precise date (it's even a plot point); 8/2/1935. But at the beginning Poirot and Hastings are playing Monopoly, and right there on the board you can distinctly read; "Trade Mark - Pat.app. For Nº 3796-36." As signaled by the last 2 digits, it's a 1936 edition (the UK localization of the game). (00:01:40)
Audio problem: In the very first turn of Monopoly shown, the player scores 11, but moves just 7 ticks. In the second, a 9 produces 8 ticks. (00:01:40)
Suggested correction: It is entirely plausible that a player does not tap the piece to the board with every move. Sometimes, you tap it hard enough to make a sound; sometimes, you just hover the piece over the square.
Factual error: In Poirot's study, Lord Pearson shows the big piece of mineral, saying "You're left holding a a nugget of top-grade 24-carat silver." That's a laughable blunder, from a top level banker and investor about to do a massive mining deal even. Silver purity is expressed in millesimal fineness. (00:11:30)
Continuity mistake: His Bankship visits Poirot during the evening, and begins telling him the story of the silver mine. "For half a century, men have died", he says. Poirot has the magnifying lens in the right hand, but also the rock in the left; cut to a different angle, the hand with the rock is held low, out of frame, and then back to the first shot, with the rock exactly where it was. (00:11:55)
Factual error: One of the two police cars identified as Unit 10, is appropriately enough, a Sunbeam-Talbot Ten. The episode is set in 1935 though (with amazing accuracy for some details, including the poster for the movie "George White's Scandals 1935" shown before the car tailing starts), and that car was manufactured only after 1937. (00:19:55 - 00:22:00)
Continuity mistake: Poirot opens the "intolerable" letter Miss Lemon hands him; camera in the door and he has his finger between envelope and letter, reverse shot and he is holding them parallel together. (00:33:45)
Continuity mistake: Poirot reads the telegram after the opium den raid. The letter is in his left hand, but moves between shots to the right hand. (00:40:40)
Audio problem: There's a bit of a mix-up in the codenames of the cars who chase Reggie Dyer. Unit 7 is the first to give chase and it is identified by its crew with the photographer. Then Unit 8 intercepts at the rendez-vous point. Check the license plate; FVW 49. Japp mentions a "unit 10" that is not shown. Later in Chinatown, Japp calls for the other cars, and "Car 8" responds, but its license plate is now YD 8501 and it's another car model. Unit 10 is again not shown. They dubbed in the wrong voiceover, they should have kept offscreen the second response by Unit 8 and made it Unit 10's.
Other mistake: Japp manages to coordinate the pincer action of the 3 police cars using a very broad map and no real information about the whereabouts of the suspect. The whole scene is rather silly, it would work in a modern thriller with a GPS, perhaps, not with toy cars and a street map of London.
Factual error: Japp in this episode uses a Humber Snipe, a 1937 model. The story is set in 1935.
Revealing mistake: As he scolds Hastings for his pancreatic hullabaloo, Poirot drinks his tisane from an empty cup. (00:02:55)
Continuity mistake: Mrs Pengelley is outraged by Hastings' question about the niece. Poirot opens his umbrella and begins to move forward to ask a different question. The left side of his coat is mostly spotless, but in the next close-up that side is instead covered in water stains, including a quite visible streak on the chest. (00:05:40)
Character mistake: The rude doctor says that Edward Pengelley "wouldn't poison his grandmother's dog", to which Poirot irately blurts out "but it is not the dog of Madame Pengelley's grandmother that has been poisoned." He should have said "of Monsieur Pengelley." (00:12:50)
Continuity mistake: After reading the will of the deceased, the lawyer folds back the first page twice in two different shots. (00:26:05)
Continuity mistake: Hastings sits down when Japp is having his meal at the inn, and eats one of Japp's sandwiches. In the rest of the scene, the sandwiches on the plate change position and Japp's beer has been replenished a bit. (00:35:00)
Continuity mistake: The level of sherry in Radnor's glass changes after Hastings smiles at him when Poirot is laying the trap. (00:38:40)
Continuity mistake: When Japp does the comical fistwave at Poirot at the end, Poirot's carriage is passing by a line of people (woman with red coat, young woman with greenish one) that already passed by when the constable was giving the 'bad news' to Japp. (00:48:20)
