Lance locks his door from the inside with a deadbolt, after the Doctor calls everybody to the meeting, and leaves through Nora's door. When they return from the meeting, he opens his unlocked door from the outside.
When Lance and Nora go back to the cellar after Lance was hit, they each enter closets next approximately six feet apart. They could hear each other clearly when Nora saw the ghost and began to scream. From the time she began to scream, the "ghost" had time to stand still long enough to make Nora hysterical and then slowly float out the door before Lance made it to her without seeing anything.
At the end of the movie when Frederick and Annabelle are in the cellar, the acid around the vat appears and disappears.
When Frederick Loren introduces each of the party guests, the back window of each person's funeral car is blacked out with a dark cloth; in all the long shots showing the procession of cars driving slowly along the road though, the back windows of all the cars are transparent with nothing blocking the view through the glass.
After Lance pulls Nora out of the way of the falling chandelier, his arm alternates back and forth from being around her shoulders to being around her waist.
Pritchard says acid "destroys everything with hair and flesh, just leaves the bones", as he proceeds to demonstrate with the vat of acid turning a dead rat into a skeleton in seconds. In fact, acid takes days to dissolve hair and flesh, and is just as good at dissolving bones. Lye, on the other hand, will dissolve hair and flesh quickly, especially if heated, and will not dissolve bones.
When Dr. Trent removes Annabelle's "hanging harness", it is just a leather bustier. A real hanging harness would have hooks to transfer the pressure from the neck to the shoulders. Such a harness was used by Darto (Burt Lancaster) in The Flame and the Arrow (1950).
The rat skeleton's floating up from the acid should not be shown held together in one piece, as the acid should have dissolved the ligaments that hold bones together, thus resulting in piles of loose bones.
When Loren says the Doctor was the first one to see his wife hanging, it was actually Lance who came up the stairs and saw her first.
When Lance pulls Nora away from the falling chandelier, she's already standing outside the diameter of the chandelier and not in any danger.
However, Lance simply reacted without regard to the proximity of danger to Nora; reactions often happen without thinking.
(at around 4 mins) As the guests arrive, they walk through the gates which are open for them. With no one behind them, the next 'clip' shows the gates closed behind them. But then again, the house IS haunted, and the gates can be seen to close by themselves after the guests have all passed through.
Frederick Loren announces at the start of the challenge that if any of the contestants dies, the deceased's heirs will get his/her $10,000. Later, he says that if any of the five contestants dies, the total $50,000 will be split evenly among the survivors. However, the initial statement is spoken directly to the film's audience, is not part of the actual plot line, and therefore, does not really contradict the terms subsequently described to the genuine characters.
Mr. Loren shakes an unopened bottle of "champagne" and points it menacingly at his wife, yet when the bottle is opened there is no effervescent "fountain" nor bubbles visible in their glasses when poured.
When Frederick shoots the vase, shattering it, it doesn't leave a bullet hole in the wall immediately behind it.
Mr. Loren fires the pistol that he gives to Mr. Pritchard. Later, Mr. Pritchard cycles the slide on the pistol (an action unnecessary on a self-loading pistol since by its very nature it loads itself using the gas from the previous firing), and whether or not he realized that the firing chamber was loaded, a cartridge should have been ejected.
After Nora brings everyone to the cellar when Lance gets locked in the room, Mr. Loren lights a candle when he goes to enter, but the room itself lights up before he even enters the room.
When using candles in the rooms in the basement, the candlelight is obviously a spotlight as the shadows of the candle and silhouette of the person are displayed on the wall, when all there should be is candlelight.
Even though the "ghostly acts" are a set-up between Annabelle & Dr. Trent through most of the film, there is no explanation on how the two of them could have set up a gag where Annabelle is hovering outside the second story of the house & starts to come closer to the window as it's thundering & lightening outside as well as having a rope come darting in through the window and coiling itself around Nora's feet. That would have taken a lot of time, at least a two story structure or crane to rig up as well as someone pulling on the rope that slithers up to Nora & a multitude of equipment & extra helpers. If Dr. Trent was working the rope he would have had to been on the ceiling in order for it to wrap around Nora's legs which he obviously wasn't.
The house is supposed to have been built in the 1850s, and the interiors are typical Victorian-era mansion sets. The exteriors, however, are of a house designed in the 1920s by Frank Lloyd Wright, which still looked very modern when this film was made more than 20 years later.
The landing in the upstairs hall keeps changing. When it's first seen, it's just a blank wall. When Nora sees Abigail's body, there's a picture on it behind her. When Abigail is taken down, there's suddenly a door there to a bedroom where her body rests on a bed, and later when everyone retires to their beds, it becomes a blank space as if it were a hall going somewhere.
When Frederick Loren goes upstairs for the first time, he turns left to go down the hall, revealing the doors to the "bedrooms" are actually opening to the empty space of the front hall.
Frederick Loren leaves Annabelle in their bedroom, and she turns up in a room in the front of the house beyond the parlor. The downstairs room is on the opposite side of the mansion and isn't revealed as connected to the upstairs yet, she emerges in the parlor without passing them to the adjoining room.
When Frederick Loren visits Lance and Nora, there are walls to the right side of their doors that weren't there when the interiors were revealed.
After Nora throws everyone out of her room and the others are talking in the hall, someone's hand comes into the shot in the lower left corner of the screen.
When Frederick Loren visits Dr. Trent in his room holed up to the night, Trent says he has only heard footsteps and organ music, yet Nora Manning has been screaming her head off just minutes earlier.
It's unexplained how the rope floats through the window and wraps around Nora's feet and then unwraps itself and goes out the window again, especially because Nora would have seen or felt if there was a string attached.
There was not a sufficient amount of time for Annabelle to move from outside the house scaring Carol as a floating "ghost" to inside the house to arrange her fake hanging over the staircase to be discovered by a panicked Carol immediately after.
In the living room, they discuss that it's impossible for Annabelle to have hanged herself because there was not anything for her to get up on to jump. However, minutes earlier when the body is seen hanging, there is a newel post on one side and a handrail on the other, both within jumping distance.
When explaining about the house, Frederick Loren says there's no electricity, yet the lights shut off after a particularly loud crack of thunder as though there is a total blackout.