Other mistake: Mrs Vanderlyn holds a letter out of the car window and calls to the chauffeur to take it. She calls him "Dixon" but the subtitles read "Gibson". (00:37:05)
Other mistake: Miss Lemon reminds Poirot of the dentist appointment he has at 11. Poirot then receives a phone call from Japp. It turns out during the investigation that the police broke into the apartment at 10:45. Considering that at least a preliminary examination needed to be made and at the time of the phone call Japp was in his office and Poirot was still comfortably having his tisane, everything leads to believe that the dentist appointment should have been later in the day (or the events at the Mews sooner). (00:03:30)
Other mistake: At the end of the episode, the clock Poirot presents to Miss Lemon is pointed exactly at 3:28, which would be the time of the murder in the original novel, not in this adaption, when it was changed to 12:28.
Other mistake: When Hastings pulls Poirot's slip of paper out of his pocket, he's reading it upside down - as you can see from the close-up, the torn up part should be at the bottom, not at the top. (00:11:40)
Other mistake: At the very end of the episode, Miss Lemon stops talking as if she could see Poirot glaring at her above the newspaper - while in fact, he is facing the other way.
Other mistake: This adaptation opens with a nice fake Pathe Gazette news reel. The voice says that "last year" Farley sold a record 5 million pies, and that the new wing of the plant is due to open. At the inauguration, there's a banner behind him saying "1885-1935" and he's saying that in 1935 they sold more pies than at any point in their history, and he gives the kind of speech you give at the beginning of a year, trying to set a new record while still on the hot trail of the previous. At the same time, Miss Lemon tells Hastings that the typewriter broke 'last Easter' and she burst out with Poirot that she has been complaining 'for the last six months', which would put the event at the end of the year.
Other mistake: The man in front of Poirot in the line to embark argues supposedly in Italian with the officer: he does it in broken Italian but trying to pronounce informal words (even an incredibly explicit and vulgar curse at the end!) with unnatural cadence and a very thick Spanish accent. (00:28:30)