Revealing mistake: In the scene when the main character is in the library on the internet, she goes to a couple of websites. When the shot shows the URL up top, it is C:\windows98\mydocuments\etc.html. Instead of actually searching on the web they used a premade html page and accessed it from their computer.
Other mistake: After Michael kills Laurie at the beginning, he hands the knife to the inmate with the clown mask. The next kill is the cameraman for which he uses the tripod ends. A few scenes later they show Michael standing holding a knife with fresh blood on it. He hasn't killed anybody with this knife yet so where did the blood come from?
Continuity mistake: Near the beginning of the movie, Milla Jovovich reads a note that has been left on the desk. She didn't write it, as they demonstrate in the film. However, when they do show the person who wrote the note composing it, the handwriting is different from that in the note from the earlier scene. (00:10:20 - 01:12:25)
Continuity mistake: In the scene where the townspeople are fleeing to the mall there is a shot of the Deputy driving the car. You can see the top left hand corner of the windshield is covered in green goo, but when you see them parking the windscreen is completely clean. (01:03:35)
Other mistake: Towards the end of the film, after Snipes beats the crap out 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: Watch the scene where Frank gets killed. In the last shot of this scene, we see a soldier standing over the dead body. Keep an eye on the right side of the screen as the camera slowly moves away and you should see one of the cameras and a cameraman on the ground next to a large metal object.
Factual error: The rifles the British soldiers carried in the film were Lee Enfield rifle No.4's, these did not go into production until WW2. They should have been using an earlier version of the Lee Enfield rifle.
Continuity mistake: At the beginning of the film, the little boy has big brown eyes. 19 years later, when the boy is shown as an adult in the diner, he has big blue eyes.
Factual error: When May cuts her eye out with the scissors at the end of the movie, the fake eyeball used for the effect is perfectly round. A human eyeball is far from being perfectly round.
Revealing mistake: When the megalodon attacks the yacht the party goers jump off the yacht, and some of them reach the large round safety raft. To the raft's right, there is a visible yellow line attached to it so it doesn't drift away for the shots.
Plot hole: The dead young girl who wears white has hemophilia (uncontrollable bleeding), and her mother states that she's scared of all sharp metal objects (scissors, etc.), yet she goes to play in an old abandoned steel mill all the time.
Continuity mistake: In the scene where Stallone is chasing and shooting at the killer in the factory, he bursts through a door and shoots the hanging body of the FBI/SWAT officer. In the first shot of the officer you can see his lips. The next shot of the body shows that his mouth is duct taped.