Hercule Poirot's Christmas - S6-E1
Character mistake: After Japp's arrival, when Poirot walks up the stairs with the two male detectives, at one point he says "Mais no madame." ("But no mylady.")
Character mistake: In the hotel lobby, Poirot, indignant of Hastings' attitude towards the murder case, says "After three attempts had been made at the life of M. Nick, Poirot gave his word he would protect her." But he did that after four attempts; Nick already avoided 3 "mysterious accidents" (painting, car, boulder) and Poirot witnessed the 4th, the bullet that pulled him into the whole case to begin with. (01:02:20)
The Adventure of the Western Star - S2-E9
Character mistake: While handing Mademoiselle Marvelle's letters to Hastings, Poirot calls him "Chief Inspector". (00:06:55)
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)
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)
The Adventure of the Cheap Flat - S2-E7
Character mistake: Bernie Cole "King of the clubs" greets Miss Lemon and tells her she'll find Elsa "Straight down the corridor, second on the left." So she opens the second door...on the right. And it's the correct one. (00:30:50)
The Disappearance of Mr. Davenheim - S2-E5
Character mistake: The magician's assistant wears a costume that leaves her legs exposed, and the costume itself vanishes. The trick can't go as Poirot describes to Hastings and Japp (and it is made with a TV editing trick). (00:07:05)
Character mistake: As Poirot reconstructs the facts in the flat (and he explicitly says "consider the FACTS"), he lays out that "a letter which was found at the scene of the crime with John Frazer written on the bottom." But the letter simply said "Frazer", the first name was just Japp's random conjecture based on the initials on another evidence being J.F. (00:27:40)
The Adventure of Johnnie Waverly - S1-E3
Character mistake: Contrary to the short story, here Mr. Waverly consults Poirot not accompanied by his wife, and by his own initiative without even telling her at first. Given the solution of the case, this appears to be completely illogical.
The Adventure of Johnnie Waverly - S1-E3
Character mistake: When the ever gallant Poirot meets Mrs. Waverly, David Suchet hesitates for a second awkwardly as he mistakenly went for a handshake when Julia Chambers offered him a limp downturned hand instead. Not quite the kind of social faux pas Poirot would be caught into. (00:11:55)
Character mistake: Somehow, Poirot is the first person to get to the basement - he obviously would have slowed down terribly the policeman and the young and spry Jimmy rushing down the stairs with him.
