Continuity mistake: At the very start the priest holds up a crucifix and says the men will need them. The way the crucifix is held changes instantly. (00:02:00)
Continuity mistake: At the beginning when Broom is bandaging his wound, a soldier asks him about Hell. Broom turns to look at him, but in the next shot is facing forward again. (00:10:25)
Continuity mistake: When scraping the snow off thee wall at the start, the amount of snow changes drastically and instantly. The lines of the engraving are clear of snow instantly. (00:14:30)
Other mistake: All the time that Abe has been underwater reading multiple books at a time, he's never designed a machine to turn the pages? Even a pointer on a long arm would work serviceably. (00:19:50)
Continuity mistake: When Professor Broom is feeding that thing in the tank rotten eggs, you see him pick up one egg and put it in the tube. When he pushes the tube up in the next shot, you see more than one egg in the tube. (00:20:00)
Continuity mistake: In the truck on the way to the library, Abe rises and says, "Outside...with her," and gestures. In the next shot, he's hunched over. (00:25:50)
Continuity mistake: Hellboy's oversized "Samaritan" revolver is shown to only hold 4 rounds. Yet he fires more than 4 times without stopping to reload during his fight with the first Sammael creature in the museum. (00:29:50)
Continuity mistake: When Hellboy punches the car in the street, watch closely: he knocks the bumper off, it moves in the direction of the car, yet it never hits the ground. (00:32:30)
Continuity mistake: Kroenen kills the two museum guards on the balcony and they flip as they fall. The shot on Kroenen shows both landing facing up (use slowmo to see ties) and they bounce with their toes pointing up. In the next shot showing Kroenen and the other guards, the dead guards are facing down. (00:41:35)
Other mistake: Every time someone gets skewered through with a blade in this film there's never any blood on the blade afterwards. (00:41:50)
Revealing mistake: When Hellboy is filing down his horns with the small razor/sander contraption, you can tell the small sparks coming off are not coming from the contact of his horns and the sander, but rather are coming right out of the sander, revealing it is a prop. (00:48:20)
Continuity mistake: When Hellboy is walking at one point, holding his gun up in his left, gloved hand (just after one of the agents has said "This place is like swiss cheese"), watch the frame. It switches suddenly so his right hand (the stone one) is his left, and he's holding the gun in his "right." (00:59:40)
Continuity mistake: In the scene where Abe Sapien is investigating the cistern for Sammael's eggs, the cord holding the reliquary Hellboy gave him is cut and it falls out of reach. A few shots later, when Abe is frantically swimming away from Sammael, the charm can be seen still attached to his right-hand wrist, following his movements as if still attached to him. (01:01:30 - 01:02:30)
Continuity mistake: After Liz arrives at BPRD, Myers gives Hellboy chili and tells him that nachos are on the way. A dark cat is walking up to Hellboy's left side on the bed. In the next shot, the cat in that place is black-and-white and facing away from the camera. (01:08:35)
Continuity mistake: When Liz goes to tell Hellboy that she is going out with Myers, her arms change from at her stomach and shoulder to at her sides between a shot from behind and the next front shot. (01:09:00)
Continuity mistake: On their date Myers tells Liz that Hellboy loves her. She looks up into his face, but in the next shot she's looking down again. (01:11:20)
Continuity mistake: When Rasputin is talking to the professor about the evil in him, his hand ripples. From the front, his small finger is mostly straight, but in the shot behind, it's mostly flexed. Cut back and it's straight again. (01:17:40)
Revealing mistake: When Professor Broom's coffin is being carried, it is raining, and the camera is overhead, no rain falls in the centre of the picture, as the camera is in the way. (01:20:00)
Continuity mistake: Hellboy tosses Dr. Manning through the quickly-closing door to escape the pendulum on the bridge - he barely makes it under. Hellboy then spends thirty seconds dodging the pendulum, but when he dives for the door it's still closing at the same point and speed - just enough for him to pass. (01:30:55)
Continuity mistake: In the chapel at the end, Ilsa punches Myers and looks down to her right at him. Next shot is over Hellboy's shoulder, and she's still looking down in the background. Cut back to her for several lines and she's looking up and to her left. (01:41:00)
Answer: The internal machinery that powers him is clockwork. It needs to be wound like a watch every so often. He releases most of the tension when he fakes his death.
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