Question: How did blood drop reached Marta's shoes, even though it was too far from Christopher Plummer in the suicide scene? (00:53:50)
Answer: The rationale is that blood can travel quite far from an artery and her shoe therefore got the droplet on it even from the doorway - however it does seem to me that the filmic portrayal is lacking, since you don't actually see any instance of spray. Rian Johnson' script says "Blood gushes." What we see in the scene is that it is trickling down his cut - a bit.
Question: In the flashbacks of Ransom storming out, it's different each time. The first time his Grandma speaks, the second time she's silent, and the third time she's holding cake, when she wasn't the other times. The flashbacks we see don't contradict each other, they're not really portrayed as coming from unreliable narrators, they're generally an honest portrayal of what happens, even when what they're telling the police isn't what we see happen. So why these minor, certainly deliberate, differences? Far as I'm aware it's the only time it happens too, not like there are lots of moments like this.
Chosen answer: She is holding cake all 3 times, actually, so the only difference is that the first time she speaks. It can be a case of unreliable narrator, but I'd write it down as a mistake (deliberate, probably, as the phrase is important for the plot and they didn't want to hammer it in), since as you said, the other times even when they tell things to the police in a different way from what happened, the details tend to stay consistent, except for parts that are obviously made up, such as who is putting down the birthday cake for Harlan Thrombey therefore appearing subservient and not as close (when Richard tells the story, it's Walt and his wife, when Walt tells the story it is Richard and his wife).
Answer: Each time, it is being described by a different person. Maybe not all heard her speak.
Question: How come Ransom did not realise that Marta had not given Harlan the morphine when he went back to the study room to switch the evidence?
Answer: She didn't drain either of the vials so unless he actually measured how much of each liquid there was to start with, he was unlikely to notice that the amounts weren't quite what would have expected. He knew enough to know that the switch could lead to a death, but he's not anal enough to note every tiny aspect of the situation to verify that nothing's gone wrong.
Question: Why didn't Mr. Thromby feel any effects from such a large dose of morphine via IV? Wouldn't he immediately have a reaction? (00:36:30 - 00:37:00)
Answer: Thromby had actually not been given an overdose of morphine like he and Marta had thought (this was a key twist in the plot). Even if he had, the full effect would have taken 5 to 10 minutes anyway, by which time he had already cut his throat in anticipation of the "overdose" which would not have actually happened.
Question: Why do we see belisha beacons (striped black and white poles topped with orange light to show pedestrian crossings in UK) during the car chase? Are they seen on USA streets?
Answer: Those were just lamps that had a yellowish globe. The poles aren't black and white striped, they're solid black. They have a sign attached to them, probably a no parking sign, though that may make it look like a white stripe.
Answer: To add slightly to the other answer, evidently some of the blood in the scene had to be digitally removed for the film to secure a PG-13 rating, which explains why we don't see any actual spray/gush. But we are to assume that a drop managed to splash onto her shoe when he slit his throat.
TedStixon