In Istanbul we hear a muezzin giving the standard Muslim azan (call to prayer) in Arabic: "Allahu Akbar! Allahu Akbar!" However, the movie is set during the 1930s when Mustafa Kemal Atatürk was in power. During this time, the Arabic azan was outlawed, and a Turkish one ("Tanri Uludur!") had to be used instead. After Ataturk's death in 1938 the law was repealed.
The musicians in the restaurant in Istanbul are wearing fezzes. The film is set in 1935, ten years after Mustafa Kemal Ataturk banned the fez in Turkey.
The British officer who escorts Poirot on the ferry thanks him for saving the honor of the British garrison in Jordan. The Kingdom of Jordan did not exist until 1946. In 1935 it was the Emirate of Transjordan.
At the train station, the oriental women wearing kimonos are clearly made up as Japanese, but can be heard speaking Cantonese.
In the train station, we see Ataturk's (founder of independent and modern Turkey) poster on the wall, but in the 1930's, Ataturk was alive and had great power. Posters of him were only put on the walls years after his death.
When the rescue locomotive arrives to push the snow away, (time frame 2:04:17) you can see the snow is flowing smoothly like a liquid, some even floating in the air. It is quite obvious that the snow is really foam from soapy liquid.
As Poirot goes to leave the car after announcing his solution to the murder, Pierre is shown opening the salon door, and holding it open as Poirot pauses in the doorway, turns and watches as the various passengers make toasts to one another. Pierre is the first to step up and raise a toast with his glass of champagne. But when all the toasts have been made, Poirot is shown still standing in the doorway, then turning to exit, even as Pierre (actually just his arm is visible, but it couldn't have been anyone else) is seen in the exact same position, still holding open the door for Poirot.
When the conductor's uniform is discovered in a suitcase, the hat changes positions between shots.
Whilst passengers are boarding the train, you can hear through the speakers in several different languages where the train is going to stop. Sofia, Belgrade, Zagreb, Brod, Trieste. The city of Brod between Zagreb and Trieste is in Slovenia and not on the railway line. The train halt is at Slavonski Brod located between Belgrade and Zagreb.
After Mr Beddoes stabs Ratchett, the knife is seen to be clean and shiny.
Early in the film, when the Count and Countess walk past the window of the train car, the scenery outside moves vertically for a quick second, as only a film playing outside a set would do.
When Hercule Poirot is interviewing Edward Beddoes (John Gielgud) about Signor Foscarelli, the valet puts his glasses on twice on two successive shots.
When Col. Arbuthnot is explaining his "relationship" with Miss Debenham, he refers to his wife as his "Memsahib." Except that he pronounces it the way it's spelled: "mehm-SAH-eeb". A real officer in the Indian Army would pronounce that word as "MEHM-sob."
The film uses a French Railways (SNCF) Class 230G locomotive, including at the departure from Istanbul Sirkeci station, but locomotives on the Orient Express were provided by each State Railway system, and were usually changed at national borders. Only the carriages, not the locomotives, would have worked right through between France and Turkey.
The film takes place in 1935, but many of the extras (in the Turkish restaurant, at the railway station, etc.), and even actor Michael York (playing Count Andrenyi), have long, 1970s hairstyles.
During the interrogation of Colonel Arbuthnot, the reflection of a boom mic can be seen in the glass room divider behind the Colonel.
After the conspirators stab Ratchett, Pierre "cleans up". He puts the blankets back over Ratchett's body, closes Ratchett's door into the passageway outside, locks it, and chains it - all without wearing gloves. Whilst his fingerprints would be expected to be on the doorknob and possibly even the door lock, there would be no reason for his fingerprints to be on the door chain.
Just after Poirot sips his liqueur (the green drink) in the dining car, a blurry white sedan can be seen zipping across the landscape in a way that cars do not move in the 30s. It appears to be a sedan from the 70s.
The film takes place in 1935. Not only is the French locomotive incorrect, but it bears a SNCF number. The SNCF was not formed until 1938 when the French railways were nationalized.
On the final credits Princess Dragomiroff played by Wendy Hiller is marked as Wendy Miller. Colin Blakeley's name was, unlike in the opening credits, spelt correctly this time.
In the scene, when Poirot sees the woman in the Kimono passing by, the woman leaves through a door. When she closes the door, crew members are visible/reflected in the mirror panel of the closed door.
When Poirot uses the hat box to decode the burnt paper, in one shot Poirot places his small burning lamp to his right. In the next shot, the lamp is in the center ready for the hat frames to be placed over it.
When Hardman introduces himself to Foscarelli and Beddoes, he tells them to "call me Dick", indicating that his first name is Richard. Yet his name, as Poirot points out during Hardman's interrogation, is Cyrus B. Hardman.
In the credits at the beginning of the film Colin Blakely is wrongly listed as Colin Blankey.
The rescuing locomotive appears to be a Class 141R, a type of locomotive built in the USA, and not introduced until 1945.
A number of extras who play beggars at the train station look directly at the camera and smile and laugh.
When Poirot gives Ratchett the cigar lighter and they start to talk, Ratchett's left arm is resting on the table when seen from the side, but raised with his hand close to his face when seen from in front.
As Bianchi (Martin Balsam) is walking away, Poirot asks him how many passengers are in his car. He responded "Just Mr. Bianchi and I."