Factual error: The mysterious venom used to perpetrate the murder comes according to the English coroner from a "Vilitilio Occius", said to be a horn viper. Nothing wrong with artistic liberties making up animal species, but the name itself appears to be pseudo-latin with no real meaning or any closeness to other snakes, so not a particularly believable one.
Audio problem: When Hastings is caught off guard by the premature launch of the clay pigeon, he fires a couple of shots in a haste. Fairly obvious that he does not, and the mere sound of it has been added in postproduction. (00:01:40)
Continuity mistake: As the future victim scoffs saying "Must be a great solace to you" to the Tollivers, his hand goes from midair to the teacup between shots. (00:11:30)
Continuity mistake: Mrs Clapperton puts down the score notes and pencil before lighting up her cigarette. Between the shots and the reverse, the pen disappears and the notebook changes position. (00:13:35)
Continuity mistake: Clapperton demonstrates how he can deal cards of his choosing at will and therefore he refrains from playing bridge. In the close-up of his hand and table you can see the cards he dealt are stacked irregularly, but when he deals the last 4s the cards are more neatly arranged, spread in a fan. (00:17:10)
Continuity mistake: When Mr. Russell interrupts Hastings' plans of randomly shooting in the middle of the Alexandria harbor, an empty brandy glass is on the table next to him in the first shot, and comes closer the second time he's in frame. (the two shots are not strictly consecutive but there's no reason why the frail old man, still in the same position both times, would pull his empty glass a couple inches closer when off-camera). (00:26:20)
Continuity mistake: When Miss Henderson gets back aboard, the same extra (bearded man with black robes and brown belt) walks by coming from both directions at once. (00:26:30)
Plot hole: In the original novel, the victim's voice is described as "shrill." In here, it's quite the opposite. When the trick for the alibi is performed, the relevant lines are not read by John Normington, thus Poirot's exposition at the end, with the girl providing the voiceover, indirectly further exposes its unbelievability.
Continuity mistake: When Miss Lemon announces the anonymous caller to Poirot through the window, she holds the receiver at noticeably different heights between the consecutive shots. (00:09:00)
Factual error: The basis of the blackmail is based on the Japanese invasion of Manchuria because howitzers were supplied to bombard Shanghai. Shanghai is not in Manchuria. (00:35:41)
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)
Continuity mistake: Poirot is holding up a letter in an envelope. He turns it to show the front to Lady Mayfield. The flap of the envelope appears to be tucked in. The shot cuts to a close-up, but now the back of the envelope is facing Lady Mayfield and the flap is sealed. He then turns the envelope to show her the front. (00:44:20)
Factual error: The machine guns on the plane appear to be cannons, which were not introduced until much later.
Plot hole: Hastings came over to assist Poirot in his case, posting guard overnight. He offers to drive Poirot back to the villa since Poirot is in a rush and has figured out of the culprit. Poirot approaches the villa just in time to come across Mrs. Vanderlyn on her way out. Poirot rushes to Hastings then to give chase to the woman but...Hastings has pulled out all the plugs and is cleaning the carburettor, just doing some random maintenance to the car that would take him, in his words "an hour" to bring back to work. On a one-day job, Hastings crippled their own car for no reason whatsoever. This is beyond stupidity.
Continuity mistake: Ralph Walton flubs the line and breaks character walking off set: he begins undoing his collar. He repeats the same action ('begins' to undo it) next time the camera is on him, and during a cut when he is in frame both shots, his hands jump off/on the collar. (00:04:35)
Continuity mistake: When the secretary leans in to console "Henry" after Walton has been escorted away, he pins her handkerchief hand to the desk; in the next shot the hand is turned differently and caught in midair. (00:07:45)
Continuity mistake: As Poirot, holding the family picture, turns around to ask Mrs. Oglander about the kids in the portrait, he suddenly has his finger near the middle of the frame, much higher than before. It keeps going up and down during the conversation. (00:36:40)
Continuity mistake: When Poirot stands as his employer sends him packing, the shadow projected on the back wall is taller than the cupboard by a good margin, roughly from the shoulders up. In the close-up that follows, Poirot is standing in the same spot when he replies "I shall not fail to do so", but the shadow is shortened considerably. (00:14:50)
