Continuity mistake: When Peach collapses on top of Mario after the weird TV invasion, Mario's arm is on top of hers, but in the closer shot that follows his arm is distant and in fact it is behind hers the moment he turns a little.
Continuity mistake: After Eugene takes the stage to face Jack Butler, everyone (including Eugene) turns when Scratch walks into the room. When Scratch sits down and Eugene turns back to face Jack Butler, Eugene's hat is gone.
Other mistake: Maureen cuts her wrists with a razor blade. Days later, no bandages or scars.
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: 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: 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: 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)
Other mistake: Lakella seems to disappear from the movie after the battle.
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.
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)
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)
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)
Continuity mistake: After the car accident, a man in a black hat and coat runs up to the left-side rear window of Patton's car, taps on the glass, then peers into the car. The camera angle changes to show the Jeep arriving and we see the same man in black arrive again to repeat all the same moves exactly. (01:13:30)
Plot hole: The school is supposed to be rundown and closed after ten years yet Marty somehow manages to get in, rig up all his traps (including the acid through the bath pipes), and setup the reunion supplies without the caretaker ever catching on to anything that's going on. It also begs the question if the caretaker was there the whole time until he was killed how did he not notice the other students waiting outside for several hours or their cars to ask what they were doing while outside?
Continuity mistake: During the wedding reception at the beginning of the movie, Rachel asks the bartender for "two red wines please." When she returns to her friend, she has only one white wine glass.
Revealing mistake: When Louise pulls off Joel's trousers, we see that he is wearing briefs under his boxers.
Continuity mistake: At The Incinerator night club, Lance rides past an exit on his motor bike as an ATV and its rider emerges, but when the shot changes to Lance riding down the ramp, the same ATV and rider are emerging from the exit again.