Continuity mistake: Marta goes to Ransom to tell him about the blackmail letter. During the scene, the position of Chris Evans' hands is inconsistent between shots (he suddenly has his hand under his chin in just a close-up, and he is holding the letter at a different angle when he tells Marta that the toxicity report will shot the overdose). (01:28:50)
Continuity mistake: At the end of the car chase, Marta is looking at Blanc shielding her eyes with her hand. When he says "I don't know what he came back to do" etc, Marta's hand is off her forehead, but is on in the shots before and after. (01:34:05)
Continuity mistake: When Ransom asks "Fran's alive?" to Blanc, Chris Evans has his hand raised, thumb before his lips. But the hand is lowered in the shots before and after. Similar situation when the word "Jail" is used a few seconds later. Hand visible in close-up, not matching the wider angles. (01:58:10)
Continuity mistake: At the beginning of the movie, Marta is sitting at the kitchen table with her mom while her sister watches crime drama. The arm position of her mom keeps changing during the scene. When she says "Turn it off NOW" she has her elbow on the table leaning on, and then lowers it, still keeping it on the table. In the shots before and after both her arms are off the table. (00:03:00)
Continuity mistake: When the detective (Benoit) asks Marta to be her "Watson", the wind is blowing hard enough to move their hair. In the reverse shot, it is calm.
Continuity mistake: Marta picks up the phone at the beginning of the movie. In close-up she is holding it with her left hand, but at the cut it switches to her right hand. (00:03:20)
Continuity mistake: When Ana runs out of the gates in the back yard they're left open, but when Ransom returns at 3 am they're closed. And even though it hasn't rained for a week it is still muddy.
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).
Sammo ★