Revealing mistake: When the bully's held up by Sam wires can be faintly seen.
Continuity mistake: Marjorie sprays the rapist in the left eye, mostly, with insect spray, but later it is his right eye that is affected the most.
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)
Visible crew/equipment: When Crispin Glover goes into a telephone booth to make a call, the cameraman and his camera are reflected in the glass.
Continuity mistake: When Rachel goes to the "group", her bag is multi-coloured; when she comes home from the "group", her bag is different, it is now just black.
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: Lakella seems to disappear from the movie after the battle.
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)
Factual error: The movie as the opening captions say, is set in Melbourne, Australia, 1978. However when Sam at the beginning of the movie drinks the milk and moves to the other room where the TV is, he passes by a poster (a communist party poster, the Italian communist party, strangely enough) that was designed only in 1981. (00:09:25)