Plot hole: According to the denouement sequence shown in the film, Linnet Ridgeway is shot asleep in her bed approximately three minutes after retreating from the lounge. Less than 2.5 minutes pass from the moment Linnet leaves the lounge to the moment when Doyle is left alone by the other guests. It takes another 30 to 45 seconds for him to pick up the pistol, rush into his cabin and kill his sleeping wife. How could Linnet have walked to her cabin, taken off her jewelry, changed into her night-dress, retired to bed, and fallen asleep in 180 seconds? (00:59:00)
Suggested correction: The sequence never showed when Linnet goes to sleep. We can't be sure how long it is between her leaving and Simon shooting. All we know is in the actual scene she leaves after having already taken a sleeping pill. This is "movie time", not real time. 3 mins can be 30 mins in movie time. The flashback sequence doesn't clarify anything based on her timeline.
This...is not at all what happens. This is the 1978 movie; Linnet is playing cards with the others up until a moment before cutting the game short not by her choice but because of Jackie's interference, so certainly took no pill in advance nor does she take one on screen, and the characters interact with no interruption from that point on leaving no room for an implied 'movie time' elapsing at a significantly slower rate than 'real' time.
Plot hole: Simon wasn't shot at the time everyone thinks - he shoots himself after killing his wife - so how did he get all that sweat, in his forehead, through his hair? It was all over him.
Suggested correction: He'd just been running around the boat, and he'd just killed his wife. That'd make anyone sweat.
What the OP says is that he's already sweaty before he does any of that; if you look at the first scene when he's tricking the others, and in Poirot's flashback during the denouement, it is true that the actor's face is already pretty sweaty, although not quite as much as it is later when Simon is actually in pain. Look at him when he closes the bottle of varnish, his hair is a mess sticking to his forehead. You could argue he was nervous, but in the rest of the movie he keeps his cool all the time without such displays of perspiration.
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.
Plot hole: It's not solely the adaptation's fault, but in the visual medium it sticks out more. We know that the killer used nail polish to simulate the blood the first time around, and then throws away the stained handkerchief and replaces it with a clean one which will be stained in real blood. The problem is, you see the fake blood, which is nail polish, drip down his pants and soak his hand; while the pants may not be too much of a problem since the doctor cuts them off in the proximity of the wound (even if we see a drip in the uncut part, it's likely that Poirot never took a look at them), Simon still has a hand covered in paint, which has also a characteristic odor as Poirot remarks in a different part of the movie, and wouldn't come out easily. Somehow that goes entirely unnoticed, and it wouldn't take the sharp instinct and senses of Poirot to pick up on the anomaly, you'd think. He was also of course mighty lucky that nothing spilled on the couch or carpet.
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.
