Other mistake: In the opening fight, right before the title card, Blade fights five vampires. He kicks one, who falls onto the ground and starts to crawl away. He then kills the other four vampires with his weapon (sort-of a blade that's on a line he can whip around). After those four vampires "dust," you see the fifth vampire (the one Blade had kicked earlier) on the ground... and he spontaneously "dusts" for no reason whatsoever. Blade did nothing to him... he just dies for no reason.
Suggested correction: He gets hit by the silver knife on a string (whatever it is called) like the others in 1 swing (there are 5 in total BTW). A small touch seems to be enough to dust them.
You are correct there are five (typo), but the last vampire does not get hit by the knife in any way that I can see. Watch this clip: https://www.youtube.com/watch?v=7LkxaihdyRE Blade swings the knife-line above his head (you can see the line in the entire shot), and there's never any point that I can identify where it hits the vampire on the ground. Blade swings it in an upward motion, and you can see the line goes slack after it hits the last vampire on the left side of screen, implying that it stopped and fell to the ground in that direction.
The blade goes around his head at least twice before it hits the last 2 vampires. I admit that it's unlikely but you can't really see where the blade goes unless you go into slowmotion (if that even shows anything as it's all CGI). It could have hit him at any point.
It does go around his head twice and is quite fast, but it is definitely visible throughout the shot (slow mo is not required), and at no point does it go low enough to hit the vampire on the ground. It would need to completely defy all laws of physics to do that.
