Sammo

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.

Sammo ★

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.

Sammo ★