Revealing mistake: Uhl talks about Eisenheim's childhood, and about the vanishing tree. Problem is that not only the tree disappears, but also his very own shadow, making him look as if he's floating in a landscape, thus giving away the green screen effect. (00:06:50)
Continuity mistake: When Inspector Uhl is inspecting the theater prior to the arrival on the prince, he is speaking with Eisenheim. When Uhl says "I have been puzzling over how it works", Eisenheim is standing with his arms behind his back. When it cuts his arms are crossed. (00:20:15)
Continuity mistake: Eisenheim holds Leopold's sword with a handkerchief underneath. Depending on the angle the handkerchief is messed up or folded neatly. (00:38:30)
Continuity mistake: When Eisenheim places the sword upright parallel to the floor, although it's supposed to be still, watch its blade and the design of the wooden floor and you'll notice its position keeps changing depending on the shot focusing it. (00:39:00)
Continuity mistake: When Leopold is trying to grab the floating sword, the position of his fingers on it differs depending on the angle focusing. (00:40:15)
Continuity mistake: Eisenheim ends his show to Leopold and the Duchess turns her head away in slo-mo. When the angle changes half a second later she is staring at him and repeating the previous movement. (00:41:45)
Continuity mistake: The Duchess arrives at Eisenheim's house horseback riding, her hair loose and messed up. She talks to him, kisses him, and a second later, when she enters the house her hair is perfectly brushed. (00:43:00)
Audio problem: When Uhl arrives as Prince Leopold is practising shooting, he informs the prince that Sophie had spent the night with Eisenheim. The prince asks Uhl whether they were 'fornicating'. His mouth, however, is saying f**cking. (00:51:50)
Continuity mistake: At the start, in shots from the stage towards the audience, all of the fires are lit, but in a closer shot of the audience near the front of the stage, at least one of the fires is out. During the final illusion shown at the end, the same shot or at least very similar to the one used at the beginning shows the same mistake again. (01:28:25)
Continuity mistake: After Eisenheim has disappeared, literally, from stage, Uhl and the policemen search his office. There, Uhl finds Eisenheim's notebook with the design of the locket in it. There is a large tear in the middle of the paper. It disappears when the inspector looks at it again after he has found the locket in the Prince's barn. (01:31:00 - 01:31:45)
Visible crew/equipment: Near the end of the film, Chief Inspector Uhl is in Prince Leopold's office. In the close-up shot when the two argue, you can view the boom mic, going from one character to the other, in the reflection on the brass table lamp.
Continuity mistake: After Eisenheim's disappearance, when Inspector Uhl finds the paper with the detailed diagrams of Sophie's locket, all of the writing and drawings are completely different in the close-up of the diagrams, later at the stable.
Other mistake: Watch the Crown Princes body after he's shot himself in the head at the end of the film. As Inspector Uhl tells the men who broke in what happened, the Crown Prince is still breathing very heavily and noticeably.
Audio problem: When the ghost boy walks up from the audience, you can hear the steps creak as he walks up.
Factual error: When Eisenheim is at the Vienna rail station, catching his train after the Crown Prince has died, the overhead electric cables of the modern railway are visible in several shots.
Factual error: When the narrator says Eiseinheim bought a theater, watch the houses on the background, on the right side of the screen. One of them has a visible modern antenna on its roof.
Audio problem: After the first night in his new theatre, Eisenheim walks towards a crowd, who ask him how he's done the trick. But none are mouthing the words.
Answer: You never see the sword closely enough to notice if Eisenheim took them during the performance. It is likely that he did not since this was a bit early in his planning (if he had started at all) and the Crown Prince could easily have noticed and replaced them or investigated that they were stolen. It is more likely than Sophie took them after the Crown Prince was passed out and then planted the green one in the stable and the red one in the folds of her dress.
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