Other mistake: At the beginning of the movie, Ginevra is reading the magazine but is interrupted by the outbreak of a thunderstorm. There is no rain at all, though, just the sound effect of thunder, with the car already wet at the beginning of the take to try to establish the illusion. (00:00:40)
Other mistake: In Trieste, Carol comments that someone should be with their mother; it seems to be a comment to the fact that she just tripped as it is shown in a wide angle. However, a conversation ensues and Ginevra at the end of it sees through the telescope...her mother trip, again. To make the event even more baffling, Ginny couldn't have witnessed the event from the promenade viewer, the angle is completely wrong. (00:08:45 - 00:09:10)
Other mistake: The ship the characters use to get to Israel from Trieste is supposed to be named "San Salvatore", but the stock footage is a repeat of the exact same ship they used to get from the US to London, the St. Louis. (00:20:15)
Other mistake: Poirot enters the office of the Royal Commission at 10 to 11. We see and hear the interactions between him and the other people, and barely five minutes pass, but the clock is a minute past 11 when Lady Westholme comes back. (00:53:00 - 00:58:00)
Other mistake: The spider scene is wildly different when Poirot narrates it at the dinner table (Miss Quinton immediately replies "Oh yes, spiders don't frighten me") compared to the actual scene (she said that replying to a different line). (01:12:20 - 01:33:40)
Other mistake: Lady Westholme leaves the room to take a call from England from her husband, Lord Westholme. When she gets back to Poirot, she mentions with outrage the call from Colonel Carbury. It can't be both, it's not even where she lives or works.
Other mistake: Poirot realises that the champagne was poisoned because he happens to notice two cockroaches sipping the spilled champagne instantly died, in fact FIVE are dead when he looks again. This is quite cartoonish; besides the fact that roaches wouldn't die that quickly for that (if they would), we are in the middle of the ballroom/party hall of a luxury cruiser; if the moment something vaguely edible happens to fall on the floor there's half a dozen ravenous cockroaches jumping on it, people have better things to do than dance; that's one massive infestation.
