In the opening scene in Jerusalem, the Dome of the Rock is shown covered in shiny gold. Although the golden dome is an instantly recognizable landmark of Jerusalem - in 1934, when the movie takes place, the Dome of the Rock was covered in blackened lead, and was coated gold only in 1959.
Even though attractive SNCF 241.P 65 was used, the Class 241 was built from 1948 to 1952, but the movie takes place in 1934. In addition while the train goes through Turkey and Yugoslavia the locomotive never changes. This would be impossible due to regulations at the time. During the trip of the Orient Express the locomotive would have been changed on every border crossing.
As the train leaves Istanbul, a panorama of the city shows the Galata Tower, a cylindrical tower with a distinctive high conical roof; however, although built in by the Genoese in 1348, the roof was destroyed in 1875, and was not restored until renovations which took place in 1965-67. For the intervening period, including during the time-frame of the movie, the tower was flat topped.
The opening scene takes place in 1934 Jerusalem, more exactly next to the Western Wall (also known as the Wailing Wall). There was no yard in front of the Wall until after Israel took over the place in 1967.
There are prominent product placements for Godiva Chocolatier in the film, however they are using the modern logo rather than the more ornate one which would be correct for the 1930s. Further, prior to the 1950s Godiva only had one store (in Brussels), making it unlikely that the chocolate would be available on a train journey from Turkey to France.
Uniform LED-like interior accent lighting seen inside the train cabin. There was no technology in 1930s that would allow this kind of lighting at that time. When the train leaves you can also see a tubular light bulbs on the wall of the final car, again, these kind of light bulbs didn't exist in 1930s.
In the Italian version of the movie, when making his offer to hire Poirot, Mr. Ratchett says: "Italians, third world!". The term "Third world" was created during the Cold War by Alfred Sauvy in an article published in the French magazine L'Observateur on 1952 referring to unaligned countries with either Soviet bloc or the NATO bloc.. long time after 1934 when the movie takes place.
Since the events took place in 1934, it's a clear mistake of the movie makers having included two recordings from 1935 ("Merry-Go-Round", performed by Duke Ellington, and "I Get A Kick Out Of You", performed by Leo Reisman), and one from 1938 ("Any Old Time", performed by Artie Shaw).
In the incredibly tight shots inside the train, there are dozens of hinges that are attached with Phillips head screws. Phillips head screws were first invented in 1930, so it is difficult to imagine they would be installed so prominently on a train in Europe only four years after their invention.
Late in the movie when Dr. Arbuthnot confronts Poirot with a handgun he employs a two handed grip on the gun colloquially know as tea cup or cup and saucer method. This method of handgun shooting was not taught until WW 2. A WW 1 military trained shooter like Dr. Arbuthnot would have been taught to shoot a handgun with a one handed grip exclusively.
In the opening scenes, one character is seen doing what appear to be martial arts kicks and moves that would not have been widespread in the early 1930s. However, he is a famous and accomplished dancer, and the moves look somewhat like ballet moves. Alternatively, he could have traveled enough to have been exposed to the martial arts.
Poirot wears an elaborate mustache protector the first night on the train. The second night, however, he doesn't, which is out of character, seeing as how he psychologically needs everything to be perfect.
The number of passenger cars changes between scenes. It is also mentioned that there is a second-class carriage, but the train consistently has four carriages, and all of them are accounted for (first-class, baggage, two dining cars).
On just about every scene Poirot's goatee has either a different shape or different hair patterns. With prominent gray hairs you easily spot the lack of continuity. This is very strange for a character that supposedly has OCD and such a prominent visual characteristic.
In the final scene at the Wailing Wall, Poirot's white pocket square is on the right side of his jacket...where no pocket exists. In the next scene, it's on the correct, left side. Then again on the ferry, it's back on the right.
Between Vinkovci (last stop before the murder) and Brod (today Slavonski Brod, the final stop in the movie) there is roughly 70km of a totally flat railroad. Nowhere near the alpine/mountain/snowy setting that it is depicted in the movie.
Hercule Poirot presents a mystery he had to solve that took place in a church. In his words to the public who came to see him in front of the Western Wall, he mentions that the church is The Church of the Holy Sepulchre, that he claims to be, in his words, "just above them". Well, the Church of the Holy Sepulchre is indeed in the Old City of Jerusalem, but in another part of it: In the Christian Quarter. Above the place where he stands there's, in fact, a different holy place: the Dome of the Rock, but that's an Islamic shrine - not a church.
Despite beautiful landscaping, that's not how it looks between Vinkovci and Slavonski Brod in Croatia. That part of Croatia (Yugoslavia in 1934.) is actually lowland and there are no hills or mountains.
Steam engines are powered by steam, generated by burning oil, or in this case coal. Steam is piped to the rail cars the heat them, and is expanded to run a generator and produce electricity. We see the cars are warm and the lights are on, therefore indicating the steam engine is under fire and producing steam. However, all shots of the steam engine show it with snow stuck to the boiler indicating the boiler is at or below freezing. Furthermore, the engine appears to be knocked off the tracks, which would result in the crown sheet of the boiler becoming uncovered of water and causing the boiler to potentially explode.
At the end of the film the Countess Elena Andrenyi tips her medication Barbital down the sink. If she had the dependency that she depicts earlier in the film, doing such a thing would kill a person in a matter of days. Barbital was a powerful barbiturate, similar to Valium but obviously as a liquid, harder to regulate, the withdrawal from a large amount to nothing would almost certainly kill anyone.
When Poirot is questioning the Count and Countess Andrenyi he looks at her Hungarian Passport. It is issued by the Kingdom of Hungary and on the inside above the Countess's name it says "Au nom de Sa Majesté François Joseph 1er". In 1934 Hungary was indeed a (nominal) monarchy but the Emperor Franz Josef died in 1916.
Although the steam locomotive shown in the film is an European model, its added effects and features only occur in US locomotives and it would hardly be found in a European locomotive: the sound of the whistle, the bell, the snowplow (seems more like a cowcatcher)
Poirot solves a mystery of a theft in the Church of the Holy Sepulchre, announcing his solution in front of the Wailing Wall in Jerusalem. Immediately after this, he appears in a port city to travel by boat to Istanbul. Although Jerusalem is landlocked in the desert, he is not supposed to be in Jerusalem, but his travel to the port city (likely Jaffa) is not explicitly shown.
Clearly in one scene an actor is seen lighting his cigarette with a classic 'Zippo' lighter (and casually closing the top). As the story takes place in 1934, it may seem anachronistic for the 'Zippo', however the first Zippos were manufactured in 1932.
During the effort to find a berth on the Orient Express, attendant Pierre Paul Michel stated passengers already booked all First & Second Classe berths or seats, respectively. Second class passengers would have a separate car from the first class passengers. The train pulled only four cars: a baggage, sleeping, dining, and bar car. During the transit and after the train stopped the film neither shows a second class passengers nor do the characters refer to them, ever.
Although most of the movie plays out in winter in the mountains, none of the characters take special precautions with regards to warm clothing, none seem to mind the cold, and none of them have visible breath as they should in such cold environment.
The goof items below may give away important plot points.
When Poirot and Dr. Arbuthnot fight, they are on the floor in an open side door in the baggage wagon, facing a great depth. In the general view of the train that follows, there is no such door, so it is either missing in the shot, or facing the other side of the train, where there is no great depth.
When the derailed train is finally put back on the rails, there is a scene immediately following that shows Poirot standing in front of the locomotive. The train is clearly still derailed in this scene, even though we saw it get put back on the rails just a moment earlier. A few scenes later, the train is back on the rails again.
Although every cabin is affected by the derailment and the sudden stop of the train -to the point that suitcases are thrown off their storage and people off their beds- Ratchett's cabin stays unaffected. Ratchett himself is nicely tucked in bed and his belongings (pocket watch, ashtray, etc) on the table.