(at around 35 mins) When Whistler looks through his infrared sniper scope as Blade and the pack walk into the first club only blade shows up with a heat signature, the full vampires show up as blue/green meaning no heat. Later in the sewer (at around 1h 10 mins), Whistler looks through infrared goggles and now the vampires show off as red meaning they are giving off heat.
Towards the end, when Blade comes out of the blood pool, he is drenched in blood and his pants are soaking wet. Within a few seconds, a group of bad guys attack him, but Blade is no longer covered in blood and his pants are dry.
(at around 46 mins) A reaper is running in the club from gun fire. The scene is shown twice.
(at around 31 mins) When Blade meets the Bloodpack for the first time, Nyssa orders them to put down their weapons. After everybody has lowered their weapon, we see how Snowman puts away his katana in the scabbard again.
In a close-up of Whistler after has speaks with Blade, Blade has jumped some distance away, where previously they were standing together (the shot of Blade walking away was cut).
(at around 1h 6 mins) Pheromones don't come from the adrenal glands.
Nomak is a "carrier" for the Reaper condition, but carriers by definition are not affected by their carried disease/gene defect, yet Nomak clearly has at least some of the traits of the other Reapers (he has their general appearance, split jaw, heart shield, and drug addict-like appetite for blood; he only difference seems to be that he has retained his intelligence).
Whistler describes the hypersonic stake gun as shooting a stake at over 6000 feet per second. The amount of energy needed to drive pure silver at that speed is in excess of 200,000 joules, far in excess of the meager 3,200 joules a shotgun produces. A gun capable of that much power would be the size of a small car.
(at around 1h) A species whose lower jaw is not functional, but merely a container for an internal proboscis, shouldn't have any use for masticating muscles. Nyssa's explanation that the Reaper's jaw muscles are "bifurcated and overdeveloped, allowing for a much stronger bite" is absurd for the obvious reason that Reapers don't bite, but sting.
There is really no way the needle glove the vampires were going to use on Nomak in the opening scene would be useful for getting blood out of the human body, because you can't reach five important veins at the same time with the needles positioned that way.
Nyssa is a "pure blood" (born a vampire) but she has a scar above her lip and fillings in her teeth. According to the logic of the movie, a pure blood vampire would never scar and, we might infer, would never need dental treatment.
(at around 45 mins) When in the House of Pain chasing Nomak, Blade tells Nyssa to wait here (in the hallway) since it's dawn outside as seen through the planks on the windows, yet it shows Scud at the same time in the plot trying to get the God lights to work on the truck since it's dark as night outside.
(at around 46 mins) When Chupa is firing his machine gun at a fleeing Reaper in the vampire nightclub he shoots two ordinary vampires, one of whom is wearing a distinctive red outfit. Then in the next shot, the Reaper has moved along the wall a little way and Chupa is still firing at it he kills the same two ordinary vampires again. The distinctive outfits make it obvious.
(at around 54 mins) When Blade fights Nomak the first time, they pass through enough daylight to cast shadows, but Nomak does not react to the light cast on him.
(at around 34 mins) When Nyssa hands Blade binoculars to see the vampire glyphs in invisible paint marking The House of Pain, he peers through the wrong end of the binoculars.
(at around 1h 30 mins) When Whistler escapes from Reinhardt thru the a/c duct and heads to save Blade from Kounen, he shoots Kounen a bunch of times thru a metal plate that has very separated holes drilled in it. It would be impossible to shoot thru those holes so many times and hit the guy.
(at around 1h 26 mins) In the Vampire HQ when Scud hits Whistler the second time, we hear the sound of the punch first before we see the hit.
(at around 1h 24 mins) When Blade, Whistler and Scud confront the head Vampire, an earlier shot of Whistler talking, but with the audio removed, is used as a reaction shot, leaving Whistler to appear to foolishly mouth a line he has just said.
(at around 52 mins) As Blade is walking across the scaffolding towards the camera, you can see the Nomak stuntman in the lower right of the shot, standing ready to be launched onto the scaffolding.
(at around 36 mins) When the group is about to enter the House of Pain, a crew member can bee seen crouching next to the door when the Bloodpack approaches it.
(at around 1h 35 mins) When Damaskinos is running towards a helicopter to escape, a camera shadow is visible across his back.
Lighthammer was bitten and for hours does not turn, yet when Priest is bitten within 20 minutes, he turns. This may indicate that the spread of the Reapers' mutated virus depends on some set of variables that may include: amount and/or location of transmission, recent feeding of the infected host, general health/resistance of the infected host, number of generations between Novak and the carrier, et cetera.
(at around 17 mins) After Whistler gets rescued he and Blade talk about how long he's been out. Blade doesn't tell him but Whistler surmises he's been gone for years. After this scene he sees Scud and says "I've been gone for 2 years." Whistler could not know exactly how long he'd been gone.