Audio problem: In the scene where everyone gangs up on Mr. Boddy, the audio doesn't match much of the action going on. (00:23:10)
Character mistake: During the conversation in the study about who is blackmailing who, Mrs. White mentions two of her five husbands: An illusionist who disappeared and never reappeared and a nuclear physicist who was found dead at home. During the last ending, Mrs. White says "So this has nothing to do with the disappearance of my nuclear physicist husband or Colonel Mustard's work on the new top secret fusion bomb?". However, during the conversation in the study, Mrs. White says her illusionist husband had disappeared and her nuclear physicist husband was found dead at home. So the correct term would be "So this has nothing to do with the disappearance of my ILLUSIONIST husband or Colonel Mustard's work on the new top secret fusion bomb?". (00:21:05 - 01:27:35)
Suggested correction: Ms. White's nuclear physicist husband disappeared too, so the line is right.
Other mistake: During the entire movie, the candles on the dinner table are lit and yet never seem to get any shorter as the movie progresses.
Continuity mistake: The Singing Telegram's body position changes when everyone finds her. (01:04:45)
Suggested correction: She was shot, not switched off. She likely didn't die instantly. It's perfectly reasonable that she would move her arm as she was dying.
She died instantly, that is why she collapsed instantly. I am still wondering why they didn't make it look like a real shot, and have blood around the area she was shot at? They made it look as though she was wearing a bulletproof vest and was shot. You can see silver, no blood.
Audio problem: In the third ending, when Wadsworth reveals his true identity, Professor Plum says, "Oh shucks." This sounds like it's been dubbed, and when watching his lips, he actually says something that starts with 'sh', but doesn't end with 'ucks'.
Continuity mistake: When Mrs. White and Miss Scarlet pick up the cook's body to place on the couch, they both grab the cook's hands and elbows. In the next shot, they have their arms wrapped around the cook's arms.
Other mistake: Even though it is pouring with rain, Mr. Green's coat is completely dry when he arrives at the manor. (00:07:30)
Revealing mistake: A visible editing flaw occurs near the beginning, after they return from the Billiard Room with Yvette. While Mrs. White is saying her line to Wadsworth, "I think you had better explain," she starts to unbutton her overcoat. Next is a wide shot of the room that is supposed to be in real time, but Mrs. White's overcoat has already been removed, and she is getting ready to lay it on a chair. Everyone is paused on their marks as if the film was spliced at the exact moment the director yelled, "Action" and no one had moved yet. (00:31:12)
Continuity mistake: When Professor Plum turns over Mr. Boddy to see where he's apparently been shot, his eyes are closed. In a flashback sequence later in one of the endings (where Miss Scarlet and Yvette are revealed to be the killers), after Plum turns Mr. Boddy over, his eyes are open instead.
Continuity mistake: When Mr. Green is showing the cop the dining room, you can see the hallway is completely empty. In the next shot, Professor Plum and Miss Scarlet are half way between the study and the lounge. (00:57:55)
Continuity mistake: When Miss Scarlet's car breaks down on the way to the manor, she gets a ride from Professor Plum. He turns the windshield wipers on and starts to drive away. When it shows the car driving away, you can see the windshield wipers aren't moving anymore.
Continuity mistake: In the scene where the cook's body is lying in the doorway, you see Mrs. Peacock squeeze in. The shot changes to somebody else, and you see Mrs. Peacock come inside again.
Audio problem: In the scene in the study where the cast gangs up on Mr. Boddy (when he and Colonel Mustard get into a fight), right when Mrs. White knees him in the groin you hear a lot of commotion from the other guests in the background. Included in this is Yvette saying "Oh no it's." (we know it is Yvette because of the distinct french accent) when in fact, she is in the billiard room recording the conversation.
Continuity mistake: When Professor Plum says Mr. Boddy might have been poisoned with the brandy that Mrs. Peacock starting drinking, she screams and drops it simultaneously. In the flashback, Mrs. Peacock starts screaming violently, and then dropped it.
Deliberate mistake: When they are bringing the Cook's body into the study, it's obvious the Cook is actually the Cook's double because she is much thinner and takes up less space in the doorway. (00:34:40)
Revealing mistake: Near the end, in the first ending, when Yvette is killing Mr. Boddy, you'll see that she stopped the candlestick above his head when she hit him with it.
Deliberate mistake: When Mrs. White is screaming after the power cut, she then says "Help me!" multiple times. It's obvious the "Help me!" lines are just a recording played over and over. (01:03:15)
Revealing mistake: When Yvette shoots the chandelier the reflections of the lights can be seen on the hall floor in the high angle shots. the lights stay still when the chandelier is spinning and falling.
Continuity mistake: When Professor Plum is sitting on the couch between the corpses of the Mr. Boddy and the Cook, Mr. Boddy is lying in Professor Plum's arm, in the next shot when Colonel Mustard, goes to close his eyes, he is now lying next to the arm of the sofa.
Audio problem: In the first ending, when it's revealed Miss Scarlet murdered four of the six people in Hill House, Colonel Mustard tells Miss Scarlet he has no more money when she wants to blackmail the guests. The other guests reply that they don't have any money either, but look closely at Professor Plum. Although Plum answers "Nor I" to Miss Scarlet, his lips are closed and don't move.
