Colonel Arbuthnot is the next witness to be called. Poirot finds his French lacking, so he switches to English to speak to him. Gathering basic details, Poirot finds him uncooperative, so he becomes, “more foreign than he need have been” to draw him out. Poirot leans on his connection to Mary Debenham, which the Colonel finds “highly irregular.”
Poirot’s command of English comes into play here, as the French of the American and British passengers is generally poor. Arbuthnot is withdrawn and hostile from the first, so Poirot leans into antagonizing him by becoming more “foreign.” Arbuthnot has been open about his distaste for foreigners. Poirot is something of a chameleon who can play up or down his foreign qualities when it suits the investigation.
Poirot tells a white lie that the murder was most likely committed by a woman, and so he must especially scrutinize the women on the train. He notes that it’s challenging to deal with the English, as “they are very reserved.” Poirot further implies that the Colonel feels “warmly” in the matter of Mary Debenham, to which the Colonel reacts with hostility.
Although Poirot doesn’t put much stock in stereotypes, he deploys a stereotype about the English to great effect, trying to anger Arbuthnot into a revelation about the case. His innuendo about him and Mary Debenham pursues the same objective: to make Arbuthnot emotional and therefore less careful.
Colonel Arbuthnot goes on to establish his movements the previous night, spending most of it in conversation with MacQueen. Then Poirot asks him to cast his mind back, setting the scene by saying “you smoke—perhaps a cigarette—perhaps a pipe” and Arbuthnot volunteers that he smokes a pipe. At one point the Colonel smells a “fruity” scent which he takes to be a woman passing in the hallway.
Poirot again smuggles an important question into a larger, unrelated question. The suggestion of smoking appears just to provide a memory aid for Arbuthnot, but it’s crucial to link him to the pipe-cleaners found in Ratchett’s cabin. Arbuthnot takes the bait, answering that he prefers a pipe, which in turn makes him a credible suspect. Additionally, the fruity scent points indirectly to the woman in the scarlet kimono.
Poirot then asks him about Colonel Armstrong, and Arbuthnot names a few unrelated men named Armstrong but remembers Colonel Armstrong after Poirot nudges him towards the correct man. When informed that Ratchett was the man who kidnapped Daisy, Colonel Arbuthnot approves of his death, but he would have preferred that it happen lawfully, as “you can't go about having blood feuds and stabbing each other like Corsicans or the Mafia.” He adds, “a trial by jury is a sound system.”
Colonel Arbuthnot, like many of the passengers, is not sorry that Ratchett was murdered. But he’s the first of the passengers to express concrete disapproval of the way Ratchett was punished. His reference to “Corsicans” and the “Mafia” is a not so subtle way to throw suspicion on the Italian passenger. But it’s also a way to express a very English aversion to vigilante justice.
Poirot asks for a recollection of any other suspicious events on the previous night, no matter how small. Colonel Arbuthnot notes that he noticed the door in cabin sixteen was slightly open so that the “fellow” inside could see out without fully revealing himself. Poirot accepts that evidence but replies “doubtfully.”
Colonel Arbuthnot speaks of the fellow in cabin 16 peering out into the hall without realizing that the fellow was Poirot himself. He had previously mistaken Poirot for another Belgian, his friend M. Bouc. It’s clear from this that Arbuthnot has some severe cultural blinders.
Colonel Arbuthnot leaves but not before vouching again for Mary Debenham, calling her a “pukka sahib.” After his departure, Poirot sums up the interview, finding it hard to believe that an “honourable, slightly stupid Englishman” would stab Ratchett twelve times. He insists that “one must respect the psychology.”
Poirot restates his focus on “psychology” as the key to detective work and notes that this psychology points away from Arbuthnot, an “honourable, slightly stupid Englishman.” Here, the psychology of the crime conflicts with the physical evidence, as the presence of a pipe-cleaner in Ratchett’s room points directly to Arbuthnot.