The Mysterious Affair at Styles - S3-E1
Continuity mistake: Poirot is concentrating in London, making a house of cards. When he says "I steady my nerves, that is all", the 6 of hearts can be seen in his right hand, and he sets it as the diagonal piece. Cut to Hastings, and then Poirot supposedly still has the same house in front of him...but it is not. Where the 6 of hearts was, there is now a 6 of spades, and the whole castle is different, with the cards pulled tighter together. Later he rebuilds the house, and he sets horizontally in the close-up a 5 of spades, which turns into the 2 of spades immediately after. (01:19:40)
The Mysterious Affair at Styles - S3-E1
Continuity mistake: After Hastings reminds him of the mantelpiece, Poirot shouts "Mon Dieu!" and pounds the table. The cards scattered on the table differ in disposition between shots when he stands. (01:21:05)
The Mysterious Affair at Styles - S3-E1
Continuity mistake: When Hastings spots Poirot from the window as he arrives for the denouement, his hand is in a different position on the window frame (left or right of the vertical bar). (01:26:55)
The Mysterious Affair at Styles - S3-E1
Plot hole: Can't fault this massive plot hole to the adaptation, but to the source material; the culprit (forgetting the stupidity of writing an incriminating letter detailing the plan to murder someone, and put it in a desk he shares with her) since there are people outside the room that are about to enter, tears the letter in 3 neat vertical strips, rolls them, puts them in the vase on the mantlepiece, and then opens the side door to slip away...instead of simply pocketing the letter and going through that same door. Nobody was going to search him or anything and could have burned it, torn it into confetti, anything, later. It takes way way longer to do what he did, which needed him to stay there in the room increasing the chances of being found out. And of course he and his accomplice do not retrieve the letter after.
Answer: He definitely says "Belgian", but the subtitles get it wrong and show him saying "American."
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