Other mistake: When they raise the temperature of the room with the facehuggers in, once the room is at body temperature, they open the door onto the much colder corridor. This would have immediately dropped the temp in the facehuggers' room.
Other mistake: When Lydia tells the ghost Nadia that she's having a "really shitty day" with her back to the camera, you can see she's not really talking and is actually putting a pill in her mouth. The dialogue was just dubbed over it. It then cuts to a different angle and we see her repeat the exact same motion as she takes the pill a second time between cuts.
Continuity mistake: Lady Raven arrives at the Coopers' place and starts talking to the wife. Cooper's watch is set to 1:35. An instant cut later it's set to 1:20.
Factual error: Whilst trapped in the basement, the two sisters pull a rug towards them to obtain some matches, then take them downstairs and light them by striking them on a rough surface. The matchbox is labelled 'safety matches' so they would not light without using the striker pad on the box. (01:12:00 - 01:14:00)
Other mistake: Irs stabbed Richard completely through his face and shot him in the torso. Although he fell in the lake, he is later shown on the shore and he is not bleeding. Head wounds normally bleed like crazy. Since he is wounded in two places, he should have drowned or bled out from swimming to shore. (01:19:51 - 01:25:08)
Visible crew/equipment: After the casting producers ask Sue her name, age, and measurements, the scene cuts to a close-up of her eyes and nose, where the reflection of the camera and light set is visible in both eyes. (00:37:52)
Factual error: She's driving down the highway, and her car suddenly and immediately dies, with no opportunity to pull off or park. When she gets out of the car, we see it sitting on the bare forest floor - not even a footpath, much less a road. 14. (00:14:30)
Deliberate mistake: When the couple tries to escape the cabin through a vent in the bathroom, for a single-level floor, the vent would not go into the underfloor crawl space. (00:47:00)
Other mistake: The car door behind the woman before she gets killed was open, then closes in the next shot. (00:23:00 - 00:24:00)
Continuity mistake: When Bobbie Jo holds up the jar with the spider in it and tells Hellboy that she got the cargo back, he is looking straight ahead towards the wall of the church. In the next shot angle, he's suddenly looking at her face. (01:29:16)
Continuity mistake: Sister Cecilia is lying on the medical bed as the pregnancy is discovered. Father Sal Tedeschi whispers, "He believes you," as the cardinal says that it's a miracle. Álvaro Morte's hand is touching Sydney Sweeney's veil. She does not move her head in the reverse angle, but when we get back to the previous, the hand of the padre is far more distant. (00:35:50)
Revealing mistake: When Professor von Franz (Willem Dafoe) sets fire to Knock's coffin, the flame jets can be seen under the casket.
Factual error: Near the end of the film, each time Harker pulls the trigger to shoot, the magazine doesn't spin to load a new bullet. This is especially noticeable when she tries to shoot the doll.
Continuity mistake: When Samira and Eric arrive at the jazz club, Eric sits Samira down and then goes outside. A drum kit can be seen with "East Harlem Best" written on the front. Right after he leaves and right before Samira stands up to plug her iPod in, a bar stool has suddenly appeared in front of the drum kit. Eric will move this same bar stool in front of the drum kit himself again later on in the scene.