Continuity mistake: When everyone is in the Library, you can see the matches in a cup on the left of the fireplace. When Professor Plum says, "Wait a minute, suppose that one of us is the murderer," you can also see that the matches are in a "V" shape. When Wadsworth walks towards them to pull the matches out, most of them are all leaning to the left side of the cup. As the movie goes on, when the cop gets locked up in the Library for the second time, the same amount of matches are in the holding cup as if Wadsworth did not pull them out and they are in a straight line. (Third time code 1:02:40). (00:44:25 - 00:45:05)
Continuity mistake: When they enter the kitchen to check on the cook, a pot on the stove disappears and reappears.
Continuity mistake: When everyone is searching upstairs and Miss Scarlet and Colonel Mustard start screaming, they all come running down. Yvette and Miss Scarlet have on flat black shoes, but right after the running shot is over, both are back in heels.
Continuity mistake: When the Armageddon guy comes to the door, Mrs. Peacock slams the door in his face, and the flier he was holding flutters out of his hand and lands on the floor. In the next shot, the flier disappears.
Continuity mistake: After Mrs Peacock turns the lights back on in the study, she drops the dagger where she is standing, by the door. A few moments later when she is screaming about the 'poisoned' brandy, the dagger is no longer there. That area of the floor can be viewed as Mr Green is calming her down and the dagger is nowhere to be seen. This is explained in one ending, as Yvette crept in and stole the dagger in between time. However using the real ending (i.e. the one where the title card reads 'Here's how it REALLY happened') then this is a massive goof, particularly as Mrs Peacock is supposed to kill the cook with the dagger in a few moments time.
Continuity mistake: When they reach the study with the dead cook's body, they stop before entering and drop her half-way into the room. They proceed to look for Mr. Boddy in the room and file into the Study one at a time. In the same camera angle you see everyone entering the study including Miss Scarlet, then Yvette, then Mrs. White. Then the camera angle changes and in comes Scarlet, White and then Yvette.
Continuity mistake: After Mrs. Peacock says "Mmm, this is one of my favorite recipes" each time the camera angle changes at the table her fur boa changes from up to down for a few shots.
Continuity mistake: The Singing Telegram's body position changes when everyone finds her. (01:04:45)
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.
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.
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.
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.
Continuity mistake: When Wadsworth re-enacts the evening, he stabs a piece of meat to re-enact the Cook being stabbed. When he stabs the piece of meat, the knife is at a 90 degree angle. In the next shot, it's in a different angle. (01:08:30)
Continuity mistake: Miss Scarlet moves to a table to open her unexpected gift. When she says "I enjoy getting presents from strange men", if you look close enough, she goes to remove the box's ribbon twice. (00:24:45)
Continuity mistake: Before Mr. Boddy turns out the lights, there is a statue a few inches below and away from the switch. However when Mrs. Peacock turns the lights back on, the statue is directly under the switch. (00:26:25)
Continuity mistake: When Wadsworth is doing the re-enactment of the murderer killing Mr. Boddy with the candle stick, he pretends to hit Mr. Green. After he says "Will you stop that?!", Wadsworth grabs him with one hand. But when he throws Mr. Green into the toilet, he is holding him with two hands. (01:11:25)
Continuity mistake: Colonel Mustard pours everyone a drink, he puts the whisky on the table and in the next shot the glass he poured whisky in is in his hand without enough time to pick it up. In addition, he puts the decanter down closer to him in the close-up, than it is in the medium long shot. (00:41:15)
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.