Plot hole: This movie adaptation adds an odd bit where an attempt is made on Poirot's life using a cobra. How in the world did the culprit manage to get a hold of a venomous snake, is never explained or addressed and goes against the carefully designed plot, since the culprit would have needed to obtain it through a third party (a member of the staff, perhaps) and that would expose them. Poirot actually says "you found another use for that serpent" but the idea that Simon actually obtained the snake before they devised the plan and somehow just happened to carry it around on honeymoon when the plan for his uxoricide was entirely different and carefully prepared, is even more absurd.
Other mistake: When Poirot questions Maggie Smith, he repeats what she said about Linnet Ridgeway "three days ago." Besides the discrepancy in dates (it was the day before the murder), Poirot at the time was dozing off on the portside deck (mrs. Ottenbourne passes him by going across) so he could have eavesdropped on the conversation in the near area, but not on that particular one which happened on the starboard deck.
Plot hole: Jackie supposedly doesn't have any money, but she seems to have enough to travel halfway around the world, following Simon and Lynette.
Suggested correction: As Jackie was plotting with Simon to kill Linnet the entire time, surely its the case that Simon had provided Jackie the funds to be able to do this so that they could enact their plan?
Suggested correction: It's not like "not having money" necessarily means lacking at that exact moment any cash, including the funds for one trip; it can simply mean your lifestyle is not sustainable and you're gonna run out completely dry or be forced to sell your remaining properties soon if you don't change anything. The novel makes it much more clear because the characters actually address it and express concern for her saying that she probably exhausted the small allowance she had for that crazy stunt. Poirot in fact in the novel suggests them initially to just let her go on until she'll eventually be unable to keep up. Back to just the movie, it's also worth noting that she is following them on that one trip, which brought them in Egypt from Venice through Brindisi, so 'halfway around the world' is relative too, it's not like she's been squandering the money in this endeavour for a long time.
