Corrected entry: In three separate scenes in the movie Marta is said to be from Uruguay, Paraguay, and Brazil.
Corrected entry: When Harlan and Marta are discussing how quickly he will succumb after she injects him, Harlan says "It's 8ish now" but we know that it has to be almost midnight, because Marta draws attention to the time as she leaves.
Correction: He means it's about 8 minutes until he dies (as in it had been 2 minutes since his injection), not it's about 8pm. He was explaining that he had 8 minutes left, and it would be a minimum of 15 minutes for an ambulance to arrive.
Corrected entry: The second scene shows Marta bringing Harlan his coffee first to his bedroom, and when he is not there she goes upstairs to his den only to find him on the sofa with his throat slashed. This does not make sense since she later tells Blanc the true story and how she saw Harlan slash his own throat. Therefore the second scene where she looks for him and then surprised to find his body makes no sense. Furthermore it is unlikely that any blood would have gotten on her shoe since she was a distance away in the doorway when Harlan slashed his throat. Unlikely that the blood would have splattered that far away.
Correction: Fran discovered the body, not Marta. Also, arterial blood can splatter a significant distance.
She was no where near his body when he cuts his throat.
Corrected entry: Ransom switches the medicine in the vials. His expectation is that Marta will look at the vials and inject accordingly. He does not know, nor can he expect, that Marta would know how they "feel" as opposed to reading the labels. If Marta had looked at the labels first, but "felt" they were wrong somehow, she probably wouldn't have given Harlan the medicine. It isn't until after she injects the medicine that she "sees" her mistake. There is no way for Ransom to have expected this outcome.
Correction: Ransom expected her to pick up the one labelled as the correct medication (but actually containing morphine). This would have caused an overdose for which Marta would be blamed, and therefore the updated will would become invalid. Instead, she did it by instinct, which led to the plot of the film, and Ransom needing to adapt his plan. He did not expect this outcome, so there is no plot hole.
Corrected entry: He switches the medication with one syringe, that is impossible. One container is emptied in the syringe and one container is full. Leaving him with one empty and one full container and a full syringe with nowhere to put it in.
Correction: It's likely that there is more than one syringe in Martha's bag.
Correction: The narration during the scene states that he used the "syringes" (plural) he found in the bag to switch the contents of the vials.
Corrected entry: Being an accomplished mystery writer and assuming that he had been injected with 100 mg of morphine, Harlan should have realised that his suicide would have been suspicious once they did the toxicology analysis.
Correction: Harlan was doing the best he could on extremely short notice.
Correction: If he died of an overdose then they would definitely do a toxicology report. He hoped that with an obvious alternative (suicide) they would not do one. Even with a lethal dose of morphine in his system, Marta would potentially be accused of malpractice, but she would not be directly responsible for his death and would (again, hopefully) be able to keep the inheritance.
He might have realised that once the family found out that he left everything to Marta, they would insist on an autopsy. Once they found the overdose, she would have been suspected of foul play.
Perhaps, but if he did not kill himself, it would be a certainty. He was trying to get the best outcome from a terrible scenario. Either way, it's not a plot hole.
Corrected entry: When Ransom interviews Marta at the diner, he has no clue that she actually gave Harlan the correct dose, yet the final reveal suggests he knew she was innocent at this time. It's only at the very end that we learn that she gave Harlan the correct dose because she can tell the difference based on the viscosity of the two liquids and only then that Ransom would have known that she was innocent. At the time of the interview at the diner this incorrect conclusion takes the audience down a fork in the plot that is totally incorrect based on this fatal mistake.
Correction: Interesting, but I am not sure I can pinpoint which part of the final reveal suggests he knew she was innocent 'all this time'? The day after the murder, he expected to see her accused of the homicide and therefore invalidate the part when she'd inherit. Instead, he hears that it's been ruled as suicide, and hires Blanc to uncover 'the truth', because suicide would be terrible for him, she'd get all the money. So he thought Blanc would reveal that he was killed by Marta, not that she was innocent. And when he got the vials back (which he needed to do anyway), he was seen by Fran, making necessary for him to kill her and implicate Marta either way. If you mean that during their conversation he figured out that she was innocent, Marta -does- say in her story and it is repeated at the end, that she thought she mixed the two vials up when they fell. So when they speak, he takes that as a fact and realises that if she really did accidentally give him the 'wrong' vial, she gave him the right one.
Correction: Actually Ransom does know that Marta gave Harlan the correct dose of the meds, at the time of the interview at the diner itself. Because Marta was forced to tell the truth to Ransom about how she mixed up the meds. Now, Ransom knows that he switched the contents of the vials. So when Marta says that she switched the vials themselves, Ransom figures out that because he switched the contents of the vials, the effect of his action of trying to poison his grandfather was nullified. The fact that Ransom knew about the innocence of Marta, is not dependent on her ability to tell the meds apart by their viscosity and tincture, but on the fact that Ransom figured out of the nullification of his act of mixing up the contents of vials.
Correction: Pretty sure that's just to show the self-involved nature of the people saying it - they've never even bothered to learn where she's actually from.