The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: Poirot holds the widow's painting for Hasting and asks "You do not see?" In the reverse angle with Hastings (obviously) not seeing a thing, Poirot's hand in frame is holding the painting differently. (00:39:15)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: The car with Poirot and Hastings enters the village. Right as the camera begins to pan to the left, notice a woman with a maroon tailleur and a powder blue hat. She walks in the same direction of the car but turns around a moment later. Several seconds after, when we see the two protagonists in the car, the same woman can be seen amongst the passersby through the back window. (00:04:15)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: When Mr. "Clarrisa" Naughton produces the manuscript to the unsuspecting Poirot, the open side of the folder is to his own right, but it ends up on the concierge desk turned the opposite way. (00:05:15)
The Tragedy at Marsdon Manor - S3-E6
Continuity mistake: Poirot slams the newspaper on the breakfast table when Naughton asks him if the accomodation "was all right." But it is turned in opposite directions at every cut. (00:14:55)
Character mistake: Hastings and Miss Lemon return to the apartment after their visit to the various suspects. Hastings though closes the door leaving the key in the hole, outside. (00:29:20)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: When Major Rich is interrupted playing billiards, the shadows on the playing table have inconsistent angles between shots. (00:11:30)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: Japp hands Poirot the phone in his office holding it with the left hand, which turns into the right hand at the cut. (00:40:10)
Wasps' Nest - S3-E5
Plot hole: There are some additions to the original short story in this dramatization, but they create a little problem since Hastings does not come with Poirot for the finale, and in fact is told to stay home in a rather demeaning way. Without Hastings, it's hard to imagine Poirot could break into Langdon's house, since Capaldi when is not playing creepy clown is a sculptor working at home; Poirot would need an accomplice to create a diversion. And, even sillier, Poirot tells Hastings to go buy him some washing soda, but he needs the soda to pull off the switch. Hastings should have joined him at least to give him the soda once Poirot has visited the doctor.
Wasps' Nest - S3-E5
Factual error: When we see the cover of Vogue magazine where Molly Deane appears, the recreation is not bad (the lettering used is not a classic Vogue one but something very similar was used for instance in August of the same year as portrayed), but the bar at the bottom gets the date wrong, putting it down as September 10th 1935, when Vogue always had 1st and 15th of the month as date of the release, no matter the day of the week. Also, it completely omits for instance the price. Would be a pretty difficult magazine to sell without that, real Vogue covers have that detail prominently displayed. (00:03:20)
Factual error: At the end of the episode, Hastings is reading a sports newspaper. The episode is set in 1935, and a weekend, but what he is reading there announces the jockey Billy Parvin substituting Fawcus riding Galdennis, and Golden Miller and the ticket for the sweeps, making the newspaper a March of 1933 one. (00:50:55)
Continuity mistake: Hastings buys a large scotch for Rupert Carrington. You can see in the wide shot Hugh Fraser with his right hand raised to give the coins to the bartender. But in the next shot, Hastings' hand is not in frame yet, and he even ends up paying with the left hand instead. (00:30:00)
Factual error: Florence Carrington is killed on the train while she is leaving London for the weekend. When Poirot and Hastings examine the newspapers she could have been looking the day she was killed, the headline of "The evening news" in Poirot's hand announces the world record set by Malcolm Campbell at Bonneville Salt Flats in Utah, which happened on 3 September 1935, a Tuesday. (00:27:40)
Continuity mistake: At the hotel, the Count is checking in. Behind him by the revolving doors you can see three people having a conversation, with one being a woman wearing a distinct floral dress and brown stole. He steps away from the concierge and the same woman is having a chat in a different part of the hotel, right part of the frame. (00:03:30)
The Murder of Roger Ackroyd - S7-E1
Factual error: A few drops of acid are dropped on a penny and the liquid bubbles (colorless liquid) as the acid eats its way through the penny. The penny is mostly copper. Any acid that can react with a copper will also produce a bright green to bright blue solution of dissolved copper, which is not the color seen. (00:05:20)
Suggested correction: Not necessarily. It depends on the acid and its strength. A weak acid may only oxidise copper to a monovalent state (Copper (I)) (which is colourless) rather than its divalent (Copper (II)) state which produces the blue solution.
Dumb Witness - S6-E4
Factual error: Spoiler. Police Sergeant Keeley tells Poirot that Doctor Grainger died of carbon monoxide poisoning. The killer turned the natural gas in the bedroom and did not light the heater. This would result in the room filling with natural gas, not carbon monoxide. (01:17:30)
Suggested correction: Surely it was coal gas at that time, before we all converted to natural gas?
The product of coal gas is still methane, which is CH4. It may contain tiny volumes of CO but the gas asphyxiation would still have come from methane, not carbon monoxide.
Factual error: Poirot smells and very carefully tastes a drink and says, "Potassium cyanide." It is impossible to distinguish between potassium cyanide and sodium cyanide (the other common cyanide) by this method. In addition, there are another less common cyanides that would smell and taste the same as potassium cyanide. (00:16:01)
The Million Dollar Bond Robbery - S3-E3
Factual error: The stock footage of the Queen Mary coming back from the US and docking in Southampton is not in black and white, and it certainly is more recent. The crowd wears colorful clothes, no hats, neon lights are used for the building illumination, and the cars parked are of modern design. It's a post-WW2 world, not 1936. (00:38:40)
The Million Dollar Bond Robbery - S3-E3
Factual error: As the title of the episode says, it's a million dollar robbery, in bonds. Problem is, as seen when the bag is loaded, the million is in 50 dollar bonds, which was the lowest single denomination for Liberty Bonds. 20,000 big bond notes would never fit in that bag, and would weigh a lot! Funny mistake, considering that the reality of 'weight' of a sum is a problem in many movies dealing with regular dollar bills, but bonds would have much fewer limitations as for the denomination of a single note (could have been a pile of bonds worth $10,000 or $5,000). (00:19:50)
How Does Your Garden Grow? - S3-E2
Other mistake: After Katrina is arrested, Mr. Delafointaine is reading about it on the newspaper. The newspaper is dated Thursday 23rd May 1935. The date is correct, the whole investigation does happen in a day, starting around 10 AM; Poirot is greeted by the couple with "Good afternoon" and to imagine that by the time he gets to their home Katrina's news (complete with picture of the arrest!) is already in a late edition of the newspaper (a local one, at that) is a bit too much of a stretch, with all the steps taken for the investigation, everything in broad daylight. (00:43:20)
How Does Your Garden Grow? - S3-E2
Factual error: Poirot and Miss Lemon go to the riding school to meet the solicitor of the deceased. Parked in the road right as the camera pans, and featured for a few seconds, is a car Morris Eight series II, a 1938 model while the episode (as made abundantly clear by the fair invite and banner) is set in 1935. (00:28:25)