Factual error: The brothers had a two-way mirror installed in the fitting room. Todd makes faces at his brother through the glass. If the mirror had really been two-way, the woman would have seen the reflection of Todd making the faces and would have known something was up. (00:19:28)
Other mistake: The end credits are plagued by the biggest compilation of spelling mistakes you'll ever see. The French cast in particular has 2 out of 2 actors with their names wrong (PallarOy instead of PallarDy, a female, Danièle, turned into a male Daniel) and so many errors in the technical cast to make some of them impossible to identify.
Continuity mistake: Martin McNamara calls his brother at the beginning of the movie and tells him he'll be ready in two minutes. When the camera cuts to a new shot, his grip on the phone changed entirely.
Other mistake: The subtitles of the international version translate a few things completely wrong, including, when the body of the warden is found, "There were three men!" instead of "It happened at half past three." (00:04:25)
Continuity mistake: Poirot met Ariadne Oliver who invites him to the "murder hunt." Poirot and Hastings then get on a boat to head there. As they sit on the boat, there are a few extras, led by an easily identifiable lady in a yellow sweater, that move up the stairs of the pier and reach the top. The boat slowly takes off, and about 10 seconds later we see the pier again, with again those same people from before just reaching the top of the stairs. (00:02:25)
Continuity mistake: To reach Poirot, Hastings walks through the Acapulco airport with two ladies (one with a white jacket, light blue skirt, updo, carries a large brown suitcase, and another one with short hair, glasses, white trousers) that are both in front of him AND behind him, depending on the camera angle. (00:01:30)
Continuity mistake: David Chiang chases the man in a purple dress at the 1985 Hong Kong Marathon. He fires a warning gunshot; if you look at the guy in the back of the pick-up that the criminal is about to hijack, he lets go off the bar twice in two different shots. (00:02:35)
Visible crew/equipment: In the opening sequence, Sammo Kam-Bo Hung is scavenging the dead soldiers (with one hilarious twist) - however, when he is holding the ring, in his sunglasses you can see several very much alive crewmembers standing. (00:02:45)
Revealing mistake: When Louise pulls off Joel's trousers, we see that he is wearing briefs under his boxers.
Revealing mistake: During the credits, Don Falcone is reading about the bloody feud between fellow cheesemaking mafia families Lombardi and Zanetti. The first article he browses is the April 7, 1985 edition of the Italian newspaper "Il Messaggero," with a bad glue-on job (the left column's font does not match the rest of the actual newspaper). He then reads about the car bombs in another newspaper, "Paese Sera." Here the prop design is better, but if you can read Italian, you can easily see that the article does not match its headline at all; it's not about a brutal mafia murder, but rather about the "sliding wage scale" referendum which was taking place in the country at the time the movie was shot, in 1985. (00:03:00 - 00:04:15)
Character mistake: When Mitch is in Borneo calling the university, a woman is holding a jug with shaving foam and a brush. A shot later, they're on the table.