Continuity mistake: Frederick picks up a bottle of champagne out of the ice bucket and shakes it a little. As he does this the foil and wire are still on top. He turns and aims the bottle at his wife, then tips it back and the foil has vanished as he now just removes the wire and cork.
Factual error: As Frederick is explaining to his guests how to use their .45 automatics, he fires one round at a near-by vase, shattering it. However, it leaves no bullet hole in the wall directly behind the vase.
Other mistake: When Lance leaves Nora to go have a meeting with the remaining people in the house and they accuse Loren of murder, his room is locked from the inside but when he returns he opens the door without any trouble.
Other mistake: In the beginning the "host" tells the guests that if they don't survive the $10,000 due them for staying the night will be paid to their heirs. A short time later he says that the entire $50,000 pot will be split among the guests who are still alive at the end of the night.
Plot hole: Even if Dr. David Trent's and Annabelle Loren's elaborate plan had worked flawlessly (framing Nora Manning for Frederick Loren's death), the fact remains that they faked Annabelle's death for everyone to see, which would immediately arouse suspicions for investigators. Even if Annabelle and Dr. Trent somehow fled the scene before the police arrived the next morning, their actions would still raise many questions that implicated them; thus, their clumsy and convoluted scheme was far from being the "perfect crime" they imagined.
Factual error: After his wife falls into the pit, Frederick casually grabs Dr. Trent's skeleton; the skeleton that only moments earlier had been submerged in acid. His hand should have been badly burned.
Factual error: In reference to the skeleton in the pit, a skeleton with its flesh burned away would have nothing to hold it together. Frederick states it is Dr. Trent's skeleton. For him to run wire through the skeleton would have been impossible in the time he had. He had only a few minutes at best before his wife came down. He'd have had to fish the loose bones out of the pit, wire them all together, attach the whole thing to the puppeteer rig, and put it back in the pit.
Plot hole: When Mr. Loren introduces his wife to everyone, he tells her, "You know Watson Pritchard of course." That can't be because at the beginning of the movie the characters are asking if any of them know Frederick Loren. No one personally knows him including Watson Pritchard. He says, "I don't know him, all the details about renting the house were done by mail." If that's the case, it's impossible for Annabelle to know Pritchard since Frederick invited all the guests without his wife's approval. (00:34:05)
Other mistake: Once Dr. Trent enters the bedroom where Mrs. Loren is lying down "dead", they begin talking. Trent says "At first I couldn't get Nora to protect herself with a gun." There is no scene in the movie where he tries to convince her to use the gun, Lance is responsible for that. (01:02:25)
Visible crew/equipment: When the severed head in Nora's suitcase has vanished, she shouts for everyone to get out and leave her alone. In the hallway when they disperse, as Loren and then Trent walk past Lance, something that shouldn't be there (it looks like fingers perhaps) pops up into view at the bottom, left corner of the screen. This is clearer in the colorized version of the film. (00:49:00)
Visible crew/equipment: After the caretakers have gone before midnight, Annabelle tells Frederick that he should get some cars for the guests, and just as she says, "Let them go home, but pay them first," the shadow of the boom mic can be seen moving above the doorway, at the top of the screen. This is more noticeable in the colorized version of the film. (00:37:05)
Factual error: At the very beginning, while Frederick is telling us about the party, he says, "There will be food and drink and ghosts etc..." Throughout the movie, there isn't a single morsel of food ever seen or offered.