Visible crew/equipment: When Blade takes Karen to the hideout, Whistler injects her and tells Blade, "I give her 50/50 if she makes it through the night." In the shot where he says this, look directly behind Blade (near the ground, next to the drawers), and you can see a piece of equipment (it looks like extra lighting, but it's hard to tell) being moved out of shot by an out-of-sight crew member. (00:18:29)
Factual error: Whistler uses a Heckler and Koch MP5SD3 to mow down several familiars at the vampire library archives, but the muzzle flash is impossibly large and bright for a suppressed weapon.
Factual error: During the subway tunnel fight the subway train takes over 60 seconds to pass by Blade and Quinn. If the train is traveling at 30 miles per hour then the train would have to be a half mile long, or 66 train cars at 40ft per car. A standard subway train is only 8 or 10 cars long.
Audio problem: When Frost first enters the conference room with the rest of the members of the house, the older member with the symbol tattooed on his forehead scolds Frost about how he's not a pureblood. In a shot down the table (probably only noticeable in widescreen), you can see the guy on the right side of the screen, but his mouth isn't moving, even though you hear him talking.
Revealing mistake: When Traci Lords approaches Blade, he tries to shoot her with the shotgun only for it to click, empty. He then proceeds to impale her with the silver stakes mounted in the end of his gun. If you look closely (probably more noticeable in full screen), you can still see the tips on the end of his stakes when she hisses at him, meaning that they're not actually inside her, even though she disintegrates in the next shot as if they were.
Other mistake: Smoke rises from Karen's collar while she's lying on the table before she's injected with allium sativum. It's the shot that ends with Whistler reading her ID badge.
Revealing mistake: When Quinn is pushing through the door after Blade has cut his arm off, the full length of the arm is visible as he pushes the door open. On the other side of the door, his arm is gone again.
Revealing mistake: In the final fight scene, Blade is fighting a bunch of guys. Before the shot goes to Karen looking down at Blade, Blade kicks a guy away, you can see the stunt wire pulling him back. (01:43:05)
Other mistake: Blade talks to Karen about killing vampires using a stake, silver, sunlight or garlic and says that you aim for the head or the heart, but when he fights his mother in the temple he stabs her in the stomach with a bone and she turns to ash.
Continuity mistake: When Frost kills the fake policeman, prior to Frost biting him there are six to seven rubber ducks floating in the water. In the very last shot where the police officer is floating dead in the pool, all of the rubber ducks are gone.
Answer: I don't think it's so much a memory as it is Blade just equating Karen with his mother in that moment. The only way to convey his thought process to the audience, though, is to show his mother onscreen.
Phaneron