Visible crew/equipment: When Mrs. Peacock turns on the cellar lights, a piece of lighting equipment is visible to the left of the screen. (00:47:45)
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)
Revealing mistake: When the cook's body is lowered to the kitchen floor, you can see her move her outstretched arm closer to her head.
Deliberate mistake: The same footage of Ms. Scarlet screaming when the cook falls out of the freezer is used when Wadsworth falls out of the freezer. (Note the cigarette.)
Other mistake: In one of the first scenes in the study, Mr. Boddy hands each guest a weapon and then proceeds to turn out the lights. The room is thrown into complete darkness. Unfortunately, there is a roaring fire in the fireplace that would have illuminated the room enough for everyone to see what was going on.
Visible crew/equipment: Towards the end of the film, when the butler is explaining 'whodunit', as he stands at the front door, quite clearly at the top of the screen a microphone can be seen following him back and forth.
Revealing mistake: After they find Mr. Boddy's body in the bathroom, Wadsworth starts shouting. A candlestick then falls and hits him on the head. Look at the candlestick when it falls: you can tell it was pulled by a string or something.
Continuity mistake: When they enter the kitchen to check on the cook, a pot on the stove disappears and reappears.
Audio problem: When they are putting the Cook's body on the sofa, Wadsworth walks by in the background and says "Careful, don't get blood on the sofa" however his mouth doesn't move.
Factual error: When the evangelist first enters the mansion, Mrs. Peacock calls him a beatnik. However, the movie is set in 1954, and the word "beatnik" was not coined until 1958. (01:15:25)
Other mistake: When a gloved hand tosses an envelope's contents into the fire, most of the papers miss the fire completely.
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.
Visible crew/equipment: After opening the doors to the lounge to let Col. Mustard and Miss Scarlet out Mrs. White says "How did you get in? The doors were locked." After this line, for the remainder of the scene, on the left side of the wall beside the chair the reflection of a crew member and the boom mic pole can be seen moving around.
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.
Other mistake: In one ending, Mrs. White is responsible for Yvette's death, yet when Yvette rushes downstairs to meet her killer, Mrs. White is still heard screaming upstairs.
Suggested correction: If Mrs. White was indeed the killer, she could have followed Yvette, then gone into the room where they meet before her. The screaming has stopped before Yvette actually gets inside the room.
That would be impossible. There is no way that Mrs. White could have murdered Yvette because Yvette is seen running down the stairs while Mrs. White is still heard screaming upstairs. Add to the fact that the power to the house had been shut off leaving it in complete darkness, Mrs. White had no way of seeing where she was going and would most likely keep bumping into things. Plus, when Yvette gets to the billiard room, the murderer is already inside waiting for her.
Suggested correction: Mrs. White is not screaming when Yvette is walking into the room (where she is killed) only while Yvette is running down the stairs. Yvette pauses for a brief moment to look into the dining room, then proceeds to the billiard room. There are many secret passageways in the home, and one upstairs could have led into the billiard-room.
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.
Revealing mistake: In the hallway, the camera pulls back from the dining room towards the front door. The camera pulls back too far, and on the floor masking tape and a different type of wood can be seen, indicating where the set stops.
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.
Other mistake: When Mrs. White enters the house, she takes off a black and white cape so she now is wearing a light coat over her dress. There is a point at which she is about to take off the coat, and with the camera angle change, she has it in her hand.
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.
