Plot hole: In the scene where she goes to her house after escaping there is no police tape on the front door even though it is a crime scene. Earlier the police searched and taped her office - it only makes sense that they would do the same to her house.
Revealing mistake: Mac and Dillon go after the Predator. The Predator is sitting in a tree, and Mac points him out to Dillon. They both agree that they see it and take position. Mac crawls underneath the alien and is killed by his laser. The Predator then sees Dillon and lasers his arm off. Dillon's arm falls to the ground with the gun firing. Quickly Dillon turns and reaches for the machine gun around his neck. When he turns you clearly see his bloody right stump and his right arm sticking out the bottom of his jacket. [Note: As far as I can work out, this has been cunningly edited out of the UK DVD version].
Continuity mistake: A few minutes after James accidentally shoots his friend, he reloads his shotgun and tells Kristen that he is going outside to look around, and tells her to stay put. He walks to the front door and as he passes the clock on the back wall, it reads 5:00 a.m. A few minutes later, Kristen walks past the same clock, and it reads 4:30 a.m.
Other mistake: Towards the end of the film, after Snipes beats up of a lot of vampires, Whistler throws Blade's sunglasses to him. They show him throw them in one shot, then in the next shot they show Snipes catching them. But look in the background at Whistler, he doesn't have the glasses, but is moving his arm like he is throwing them. The glasses must have been computer animated, and bad editing contributed to this mistake. (01:37:34)
Visible crew/equipment: When Francesco and 'she' are in the cemetery together and the little blue flame-beings gather around to watch them, you can see the wires they're suspended on several times. This is most apparent when Francesco sees the first one (moments before seeing 'she' at the fountain) and also just before they are all frightened away. (00:17:30 - 00:20:40)
Audio problem: A soda can that is supposed to be full hits the man. When the can hits the ground you can hear that it's empty.
Continuity mistake: When Frankie is about to receive the first stigmata (when sitting in the bath), a pigeon suddenly flies up. When she takes a piece of a feather that flew into the water, you can already see stigmata marks on her right-hand wrists.
Factual error: In the scene where Arthur first enters the house and starts going through paperwork, there's a shot of Nathaniel Drablow's death certificate which shows 'body was not recovered' in the box next to his cause of death. Such a thing would not be written on death certificates of the time - that box is reserved for 'Signature, description and residence of informant', a heading which can partially be seen as the camera pans across the certificate. For the death to have been registered, an informant's signature would have to have been there. (00:20:05)
Other mistake: When they encounter the first ant, the policeman runs out of ammo, but the FBI agent fires at least nine shots. Not bad for a snubnose revolver that holds 5 or 6 rounds.
Continuity mistake: On the truck cab's rear window, there is some sort of air conditioning unit installed. In some shots, such as the gas station scene where David Mann is on the telephone, or the railroad crossing scene, the air conditioning unit has a support structure to hold it in place. In the rest of the film however, there is not any support structure to be seen.
Other mistake: When Sugimura is looking for Kotohiki, he activates his scanner to see if she is nearby. The scanner shows her location, but fails to show either Mitsuko or Kiriyama, who show up quickly after.