In the scene where Mr. Green is showing the cop the dining room and kitchen, we can see diagonally across the hall to the door of the study. Just before the scene cuts, Prof. Plum and Ms. Scarlet have not left the study yet, and are not yet in the hallway. However, as soon as the scene cuts, they are both seen already in the hallway, closing the study door.
When the cop is killed, he is in the middle of a telephone conversation. However, the electricity had already been switched off. Nowadays, telephone lines operate independently of the public power grid, allowing phones to be used even during power outages. However, such has not always been the case. In the early 1950s, when this movie was set, a power outage, deliberate or otherwise, would have terminated an existing phone conversation and made new phone calls impossible.
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.
When Wadsworth is re-enacting Colonel Mustard's arrival at the mansion in high speed, a microphone is visible at the bottom of the screen. This is only visible in the Fullscreen version of the film, which has an incorrect "open matte" transfer.
Characters make references to Mrs. White's disappearing
nuclear physicist husband in each of the three endings. Of the two of her five husbands that were mentioned, one was a illusionist that disappeared and never reappeared, the other was a nuclear physicist that was emasculated and decapitated. The nuclear physicist did not disappear. Even Mrs. White, herself, makes this error. Wadsworth first introduces this mistake when the discuss her first husband, stating, "Ah, but he was your second husband. Your first husband disappeared also." This implies that her second (nuclear physicist) husband had disappeared when in fact, "He was found dead at home."
When the guests find the cook murdered, Miss Scarlet tries to grab the knife and Col. Mustard tells her not to touch it, but as he is saying the line he grabs the knife himself negating him saying that they could get finger prints since he just put all his on the knife.
When Yvette, Mr. Green, Wadsworth and Mrs. White collide on the second floor landing, Yvette and Mrs. White and wearing high heels. When they are running down the stairs, they are wearing flats. When the action resumes at the bottom of the stairs, they are wearing heels again.
When Wadsworth asks the ladies to open their purses at the climax of one of the three endings all are empty. Women don't carry empty handbags. In addition, Miss Scarlet is seen taking her cigarette case from her bag, so it at least should be inside.
When Miss Scarlet and Col. Mustard first find the kitchen-study secret passage, as they enter the study the portrait appears to be "spring-loaded" and immediately snaps back into place after they pass through it. However, later in the film when Wadsworth is recounting how it was done, he just taps the same portrait and it swings open, and stays open.
In the first ending, the flashback of Mrs. Peacock screaming about the poisoned brandy shows her shaking the glass violently and throwing it to the ground. In reality, all she did was drop the glass and start screaming.
When the guests are done searching the house, they hear Col. Mustard and Miss Scarlet yelling because they are locked in the lounge with the now dead driver. Yvette runs and gets the gun to shoot the door open, she trips on her way out of the study and shoots the chandelier and it begins to spin. The camera then pans to a shot from the ceiling looking downward on the room as Col. Mustard and Miss Scarlet are freed, the reflection of the lights from the chandelier are seen on the floor and are not spinning although the camera shot changes from the ceiling shot to a shot of the chandelier spinning and eventually falling. The reflection does not move although the lights themselves are supposedly spinning above.
When Prof. Plum first checks Mr. Boddy's body, Mr. Boddy's head is centered between the two orange sofas at least one foot away from either sofa. In the very next shot, Mr. Boddy's head is up against the orange sofa that Miss Scarlet is kneeling on.
When the FBI agent comes to the door near the end of the movie and begins speaking about Armageddon, the door is shut on him, and his "Genesis" banner is shut in the door and falls to the floor inside the house. In the next shot, the banner is gone.
When Wadsworth does the reenactment of the candle stick murder, he hits Mr. Green with it. After that Mr. Green says, "Will you stop that." Then Wadsworth grabs the back of shirt with one hand. In the next shot, he is holding Mr. Green with both hands and throws him into the bathroom.
At one point towards the end of the film, Prof. Plum is in the hall and his right collar tip is turned up a bit. When the scene cuts back to him seconds after, the collar tip is down - correctly tucked into his jacket.
When Wadsworth goes to see the cook about how dinner is coming along a boiling pot on the stove can be seen but then when she turns around and points the knife at him the pot is gone and then reappears right after.
When Wadsworth is running to help a screaming Mrs. White, he accidentally grabs the shower knob & turns it on. We see him get thoroughly soaked. But in the next shot, he is only damp when he should be dripping wet.
After the chandelier falls, Mrs. White and Mrs. Peacock are standing in the alcove at the top of the interior marble steps by the front door. In the next shot, when Miss Scarlet shows them the Motorist in the Lounge, they are standing on the floor by the Lounge doors.
The candlesticks change location on the table throughout the dinner scene in the dining room. The candlesticks are usually in the middle of the table, but in close up shots, the candlesticks are moved away from the characters to the left or right side, most likely to see the actors' faces when they talk.
A cop vehicle drives past in the rain, heading towards the house and passes a broken down vehicle. As it passes, there is a shadow of an arm that appears on the broken down vehicle. This actually occurs twice.
In the 1+1+2+1 etc scene, a large cardboard sheet can be seen at the bottom of the screen, on the hall floor. This is only visible on the Fullscreen VHS version of the film, which is presented with the widescreen mattes that were intended to hide the sheet removed.
In the final ending, when Mrs White is throttling Yvette in the billiard room with the rope, you can clearly see the free end of the rope is held at a straight angle, and is being held by a member of the crew who then drops it. In the first ending, when Miss Scarlett is strangling Yvette, you do not see any crew and the free end of the rope is hanging down on the floor, as it would be in real life.
When Colonel Mustard suggests that everyone splits up, Professor Plum says if they go into pairs, one person will be left with a killer and Colonel Mustard replies saying the murder would have to be murder victim's partner. Yvette and Mr. Green were partners, yet when Yvette is killed, no-one assumed it was Mr. Green.
When the cook is found dead, and Col. Mustard is by her head, he touches her arm, but the arm moves of its own accord, as if the actress pulls it under her head. Also, Mr. Green lays the cook's body on the floor, and then the next camera angle Miss Scarlet and Col. Mustard lay her on the floor.
Col. Mustard said that he stole essential Air Force parts during World War 2. The Air Force became a separate branch of the military after World War 2. During World War 2, what became the Air Force was the Army Air Corps. However, some returning airmen may have already been calling themselves Air Force officers - as they did in the 1946 movie "The Best Years of Our Lives."
In the last solution (see trivia entry) it is said that Prof. Plum killed Mr. Boddy/Wadsworth, however, when Mr. Boddy was supposedly killed, everyone ended up in the kitchen except for Yvette. But he was absent for about three minutes, which gave him time to do the murder.
In the third ending, Wadsworth (in a voice over) speaks of Col. Mustard splitting up with Miss Scarlet prior to killing the motorist. The visuals show Col. Mustard engaged in an argument with Mrs. Peacock. This was to illustrate the part where Col. Mustard suggests they split up into pairs.
During the scene where all the guests are eating dinner in the beginning of the movie, Mr. Green points out that all the guests excluding Prof Plum live in Washington D.C., even though Mrs. White never mentions once that she lives there. All she ever mentions is that she was married to a nuclear physicist. However, just before this interchange, Mrs. Peacock asks "Does anyone here not live in Washington D.C?" to which only Prof Plum responds.
When the lights are turned back on in the study, Professor Plum points out the gunshot hole in the wall and Mr. Boddy's ear being grazed from the same bullet. Professor Plum is later revealed to have shot Mr. Boddy, however, he sat in between the hole and Mr. Boddy, making the angle impossible for the bullet. This was later described as someone taking the gun from Prof. Plum.
At the end, They don't move the Singing Telegram's body from the doorstep and yet the "Man at the door/Cop" Must just step over the body of the girl and the body just disappears.
(Actually, they do move the Singing Telegram Girl's body before The Chief shows up the first time. After Professor Plum mentions his history with the Telegram Girl, Wadsworth says, "Well... let's put her in the Study with the others." They do so. The Chief doesn't show up until right before the different endings, which is after they've moved the Telegram Girl.)
When everyone discovers Yvette in the billiard room after she screamed, Yvette says "It's what Mrs. White said in the study. One of you is the killer.".
Professor Plum responds, "How do you know he said that?"
However, he meant to say, "How do you know that SHE said that?"
Most likely what he said was "How do you know WE said that?"
When Mr. Boddy instructs the guests to murder Wadsworth in the study, he turns off the lights and the room is henceforth plunged into complete darkness. A gunshot is heard, and when the lights are switched back on, Mr. Boddy is apparently dead, resulting in confusion over how he was killed (the bullet only grazed his ear), and who tried to shoot him. None of this would have been possible considering the fire burning in the fireplace would have sufficiently illuminated the entire room.
After Mr. Boddy shuts off the lights in the study, two loud thumps and a person groaning are heard before the gunshot goes off. This would suggest that someone was using one of the bludgeoning weapons (candlestick/pipe/wrench) before the shot was fired, but these sounds remained unexplained for the rest of the film.
The third ending revealed that Professor Plum killed Mr. Boddy because he was absent in the kitchen when everyone found the Cook's dead body for half a minute. However, Yvette also was absent from the kitchen and Wadsworth arrives in the kitchen after the Cook's body falls into Mr. Green's arms. It was never revealed where Yvette was when everyone was in the kitchen when they found the Cook dead, why Wadsworth didn't originally arrive late in the kitchen and Wadsworth never explains what he was doing to make him arrive late.
According to the final ending it was Wadsworth's plan was to invite all the guests to the house in order to kill off all of his informants, but if that was so then he should have realized his plan had failed the moment he killed the singing-telegram girl, thereby leaving Mr. Green completely innocent.
In the scene at the end when Miss Scarlet has been exposed, she has the revolver which is supposed to be empty (1+2+2+1 or 1+1+2+1). She is pointing it at everybody. You can see into the cylinders and there are clearly at least 4 bullets in the empty gun.
After Col. Mustard and Miss Scarlet leave the lounge, one of the chandeliers crashes down from the ceiling in the hallway, yet the light level in the hallway never changes. This happens once again in the ending in which Ms. Scarlet is the killer, another chandelier in the hallway crashes down from the ceiling, yet the light levels in the hallway never change. The last chandelier was visibly on when Wadsworth shoots it.
When the four men are carrying the dead Cook's body into the study, you can see it is not the same actress playing the Cook. The person (or dummy) is much thinner and takes up less space in the doorway. This is even more apparent after they drop the body and search for Mr. Boddy's missing body. When they rush back out the door, the Cook's body is taking up much more of the doorway, much more than the previous scene.
The film-makers used the same clip of Miss Scarlet's scream in the kitchen twice. The second time is during Wadsworth's explanation. Both times, when Miss Scarlet is screaming, she is holding a lighted cigarette in her hand. The first time, Miss Scarlet had been smoking. During Wadsworth's explanation, she wasn't.
When we first see a shot of the phonograph playing the song "Sh-Boom (Life Could Be A Dream", the record spinning is evidently a 78 RPM (which was typically fashionable in the 1950s, the time the movie is set). But the only other time we see it, later on (when the electricity is turned back on after the outage during which Yvette, the cop, and the singing telegram girl were murdered), the record resumes spinning like a modern-era 33 RPM.
When Yvette gets the gun from the cupboard, she comes out and trips shooting into the air hitting the rope the chandelier is hanging from. When the chandelier falls scaring Col. Mustard, it's in the middle of the floor. This is also evident when Yvette tosses the gun under it. However, in every subsequent shot, the chandelier is now close to the bench in the hallway near the billiards room.
When Wadsworth locks the Cop in the library for the second time, he is heard locking the door from the other side. Later, when the Cop is killed, the door is unlocked and opened from the other side by whoever it is revealed to have hit him with the lead pipe in the three endings. However, it is never explained who unlocked the door or who took Wadsworth's key to unlock it, as Wadsworth never mentions the key is taken from his pocket when he reenacts the events of the evening and Yvette is not mentioned as to having a door to the room. In the first two endings, when Wadsworth is said to be Mr. Boddy's butler, it is unlikely Wadsworth left the key in the door so the killer could unlock and open the door to let the Cop be killed.
In the first ending, Wadsworth mentions Yvette told Miss Scarlet about the secret passage so she could kill the Motorist. But since the six guests were invited to Hill House and had not been there before previously, it is unknown how Mrs. Peacock knew of the secret passages in the second ending, or how Professor Plum knew of the secret passage in the kitchen to the study to kill Mr. Boddy and how Colonel Mustard knew of the secret passage from the conservatory to the lounge to kill the Motorist in the third ending.
When its revealed that the (phony) Mr. Boddy is the one who is blackmailing them all, Col. Mustard jumps up to fight him. Mr. Boddy clearly pokes him in both eyes, but immediately following he inexplicably has a bloody nose.
When Professor Plum rolls over the apparently-dead Mr. Boddy onto his back to see where he has been shot, his eyes are closed. Later, in the first ending, Wadsworth talks about how Yvette listened on everyone's conversation in the Study through the tape recorder. When Wadsworth narrates that "She heard the gun shot, she thought he was dead", there is a flashback to the scene where Professor Plum rolls Mr. Boddy onto his back, but this time, Mr. Boddy's eyes are wide open instead.
In the third/"what really happened" ending, when Miss Scarlet points at Professor Plum and says he was the missing person in the kitchen when the cook was found dead, look at the dual entry doors behind her. The second door is open, showing the outside, but the door had already been closed for some time. When Wadsworth addresses Mrs. Peacock as the killer of the cook, you can see the entry doors behind her but now the second door is now suddenly closed, as if it had always been closed.
When Wadsworth reenacts meeting the Motorist and mentions having his key stolen, when look closely at Wadsworth after he says "Precisely" to Professor Plum. Wadsworth is looking at Professor Plum to his right. In the very next scene, when Mr. Green says "Wait a minute", Wadsworth is facing forward at the door and isn't looking at Professor Plum.
The first time the Chief comes to the door as the religious
guy, he sticks his reading material in the door and drops it. From that point on and in all three endings, the pamphlet isn't visible on the floor. And, somehow, in the "B" ending, when Mrs. Peacock is next to her car, the Chief has the pamphlet in his hand, before dropping it and drawing his gun.
When the guests discover Mr. Boddy lying dead on the Study's floor, Wadsworth is standing by the sofa looking on. But after Professor Plum says Mr. Boddy's dead after examining him, Wadsworth has disappeared and he is not seen again in the room. Wadsworth reappears when he leaves the Study with the guests to check on Yvette after they hear her screaming in the Billiard Room.
Ending "B" contains some brief continuity errors due to re-editing (see "Trivia" for details): The Chief has his back to the mansion when he draws his gun at Mrs. Peacock. In the next shot, the police are immediately seen raiding the mansion, and the Chief is facing the mansion. In the following shot, he is implicitly facing Mrs. Peacock as she's being arrested with his back towards the mansion again.
After the first couple of murders (Mr. Boddy - death by candlestick, and the cook - dead by dagger), the Butler locks "the remaining" weapons in the cupboard. What was it about the weapons that each one could only be used once? He should have locked all of them up.