M. Bouc speaks this quote, found in Chapter 3. The two men, sitting at lunch in the dining car, discuss the diverse community gathered on the train. This quote foreshadows the ending of the novel and acts as a very important clue in the case. When Poirot "sits back and thinks," he realizes that only in America could such a collection of people exist in one place. Knowing that Ratchett murdered Daisy Armstrong and that the murder was probably connected to the Armstrong family, an American family, this idea helps Poirot figure out the identities passengers on board the train. The quote provides foreshadowing not only because it is a major clue, but also because it reveals a possible relationship or origin of the passengers. This quote and conversation gets Poirot's imagination working, he begins to wonder how the passengers might possibly be linked. Poirot even suggests to M. Bouc that the passengers are linked because of something sinister, saying, "perhaps, all these here are linked together-by death." The quote also reveals the peculiar situation of the Armstrong family; they have come together for three days to seek revenge, will part in London and possibly not see each other again.

Mary Debenham to Colonel Arbuthnot speaks this quote, found in Chapter 1, Part 1. On the Taurus Express to Stamboul, Poirot, Mary and Arbuthnot are the only passengers aboard the train. Poirot gives the couple, acting as strangers, close scrutiny. He hears Mary say this quote to Arbuthnot when the train is stopped at a station.

This quote is a very important clue. For one, the apparent close, intimate relationship between Mary and Colonel Arbuthnot is suspicious because the two act like they are strangers. It is unclear what event Mary is talking about, what will be "over." With the unfolding of events on the Orient Express, Poirot immediately assumes the event was Ratchett's murder. Poirot's suspicions are heightened because Mary and Colonel Arbuthnot refuse to tell Poirot what they were talking about.

This quote, found in Chapter 4, Part two, is Mrs. Hubbard's undoing. Mrs. Hubbard tells Poirot that she had to ask Greta Ohlsson to check if the communicating door between she and Ratchett was bolted because her sponge bag was covering the lock. When Poirot enters Mrs. Hubbard's room to examine the weapon, he notices that the door bolt is one foot above the door handle. Mrs. Hubbard is caught in a lie that reveals her guilt. Until this moment, Mrs. Hubbard seems innocent, even a victim of the terrible murder next door to her, but this little lie implicates her in the crime.

An unknown person speaks this quote; found in the conclusion of Chapter 4, Part I. Translated from French, the quote means, "It is nothing. I am mistaken." Poirot hears someone say this quote from inside Ratchett's room the night of the murder. Poirot hears Ratchett's bell go off, the conductor responds, knocks on his door and the person inside tells him that, "It is nothing..." Hector McQueen, Ratchett's secretary, repeatedly tells Poirot that Ratchett spoke no French. Thus, it is clear that whoever was speaking to the conductor, in French, through Ratchett's door was not Ratchett, but was most likely the murderer. McQueen's insistence that Ratchett knew no French implicates him in the murder, McQueen not only knew that someone had spoken in French to the conductor from Ratchett's room on the night of the murder, but he knew it was an important element in the investigation. This is another tactical element the Armstrong family uses to obscure the case, apparently another unexplainable element in the case pointing to an outside intruder.

This quote, spoken by Colonel Arbuthnot in Chapter 8, Part two, foreshadows the conclusion of the novel and also reveals subtext of the novel. Poirot and Arbuthnot discuss the validity of the jury system, whether rules and law is better than "private vengeance." When Arbuthnot expresses no remorse or distress when he hears Ratchett was killed and even suggests, "the swine deserved what he got" and would have preferred to have seen him hung, Poirot asks Arbuthnot whether he thinks murder is better than law. Arbuthnot's responds that there shouldn't be "blood feuds," but that trial by jury is a "sound system." Arbuthnot is not referring to law; he is referring to the murder of Ratchett by twelve people claiming to be a jury. Although Poirot doesn't officially crack the case until he "sits down and thinks," it seems he understands Arbuthnot's meaning perfectly. Poirot responds like he knows what Arbuthnot is talking about, "I'm sure that would be your view."

The trial by jury system or justification of so-called "private vengeance" is a pressing subtext of the novel. Because the Armstrong's are let free in the end of the book, it seems the book endorses murder or at least the murder of murderers. The book suggests that the law was useless in the capture of Ratchett; he was able to escape because of his enormous wealth and contacts. Therefore, it is up to citizens like the Armstrong's to "right" the situation and protect society from monsters like Ratchett. This eye for an eye, Roman mentality, is certainly not what one might expect from a British popular fiction novelist like Agatha Christie. The 12-person rag-tag "jury" is not in the same spirit of "trial by jury" as known in the US; a jury is never made up of the victim's family. Murder on The Orient Express suggests that there is a law higher than that of the state, one that permits the vengeful murder of a terrible killer.