Blooper

The U-turn that Marta performs to initiate "the dumbest car chase of all time" is shown in two shots (separated by a brief cut to Blanc's reaction). In the first shot the vehicle leaves no tire marks on the road, but the second shows new skid marks on parts of the surface that had previously been driven over cleanly.

When Blanc asks Marta about how she was hired by Harlan, she seems to cross her arms from the back. In the next shot when she is speaking to answer the question, her arms are down by her side. Her arms are suddenly crossed again in the next shot. making it clear that two different cuts from two different angles are used.

The coffee mug on the tray as Fran walks upstairs is almost full, but then empty as she finds Harlan's body and spills the contents of the tray.

During the finale, while Blanc reveals the order of events, Ransom has his right arm and hand resting on the couch in one shot and raised in front of his mouth in the immediately following shot.

In the same scene, Ransom turns his head to the right in the direction of Blanc, but is suddenly looking straight ahead in the immediately following shot.

Also in the same scene, Ransom's right arm and hand are again resting on the couch in one shot, but are in front of his mouth after a cut, then on the couch again and then again raised in front of his face.

Shots of the medical examiner building burning are inconsistent with regard to both fire and smoke.

When Marta goes over Mr. Thrombey's drug regimen, she states that he injured his shoulder about a week ago. Therefore, she is giving him 100 mg of Toradol followed by 3 mg of Morphine for sleep. Toradol is only given in doses of 15 mg/ml or 30 mg/ml. In addition, one isn't supposed to give more than 60 mg/ml in a single dose. In addition, it should only be given for five days or less.

Family attorney Alan Stevens indicates that Harlan had changed his will, sealed and it made him promise not to submit it to the Court for probate until after he died. No attorney would make that promise because any attorney would know that a Will CAN'T be submitted for probate until the testator has died.

(Around 1 hrs 33 mins) When Marta brakes and the three police cars pass her, she then accelerates into the right- and turnoff lane. The nearest police vehicle reverses before becoming the first of the three to pursue her. There is no reason for that pursuing vehicle to reverse, as they could have easily made the right turn from their stopped position.

It is possible to erase a videotape with a small magnet as Marta attempts to do with the footage of her car turning of the road; however, the magnet has to be applied directly to the exposed tape, which entails lifting the flap on the back of the cassette, not just keeping the magnet & it in close proximity. Furthermore, as Marta was fast-forwarding the tape at the time, by the time she realized what she was seeing and ejected the cassette, the tape would have already spooled past that particular moment, so even if the magnet had distorted the pattern on the exposed section of tape, the police lab would have clearly seen her car turning off the road followed by a brief burst of wavery flickering/heavy static.

A person given an overdose of an opiate like morphine would most likely progress to respiratory depression and, if untreated, respiratory arrest then death. The person would not experience the symptoms that Marta listed.

No nurse would ever make an injection without checking the label of the ampule, especially not a good nurse. That is what the label is there for. And no nurse would ever inject a substance whose label says it is the wrong one simply because the liquid inside seems to look like the right one.

Nurses are human beings and sometimes make mistakes and oversights like the rest of us. You hear news stories about patients dying due to medical errors so medical professionals clearly do not always follow the correct procedures.

Early in the film it is said that Marta is from Paraguay. Later it is said that she's from Uruguay. Even later someone referred to her as from Brazil.

This is intentional. It's supposed to show that the Thrombeys are racist and classist towards Marta and think of her as being from some generic place in South America rather than a specific country.

When Marta turns on to 1209 Columbus Avenue the sign says that the road is a one way road yet when she parks up on Columbus Avenue cars can be seen travelling in both directions.

When Marta picks up the mail off of the floor, the envelope she finds is crisp and clean. When she goes into her apartment and sets the mail down, the envelope is now crinkled and damaged. You can tell it has been opened, but she continues to open it as if it's the first time. Likely the production only had one copy of the envelope and this was a later take.

The humming sound Marta's cellphone makes is one from a phone lying on a wooden, resonating surface. No phone vibrates that loud when handheld. A common error in films, done deliberately to make the vibrating audible.

The toxicology report gives the address of the Norfolk County medical examiner's office as being in Marlborough. However, Marlborough is in Middlesex County.

Marta is meant to be a good and caring nurse. However she exhibits a major character flaw. The whole plot hangs on the fact that she leaves her medicines in the house, unsecured, every evening when she goes home. This includes morphine, which is a controlled drug.

No nurse should leave morphine unsecured at a patient's house. It is only because Marta does this that Ransom is able to gain access to the drugs and swap the labels. Marta is thus guilty of criminal misconduct.

First, the detectives entrust a person involved in the case to operate the tape deck while they talk to the groundsman. Secondly, after the attempt to watch it is botched, neither of them immediately take possession of it as a piece of evidence, leaving it instead under the control of said person involved in the case.

There is an entire industry of filing claims against the estates of wealthy individuals such as Harlan Thrombey. Essentially every such estate has claims filed against it for whatever settlement can be gotten. A wealthy family, particularly one like the Thrombeys where everyone was driven by financial self-interest, would immediately recognize that the most likely client to have hired Benoit Blanc would have been someone wanting to extract money from the estate. Hence, none of the family would have consented to Blanc's involvement in the investigation, and would have refused to have any interaction with him.

Detective Elliot says, "We're with Linda Drysdale, née Thromby" but he mispronounces née as "nee" rather than its correct pronunciation which is "nay". It literally means the name you were born with, but it's most often used to note a woman's maiden name before marriage (the name she was born with).