Revealing mistake: When Selene notices the sword laying on the rocks, the sword moves up about two inches between shots, you can judge it by looking closely at the handle of the sword. (01:49:25)
Revealing mistake: When Selene is firing her guns in the floor making a circle of holes so that the floor collapse, you can see in some shots the angle of her guns are pointing all kinds of directions. Instead of making a perfect circle the holes would be spread around the floor and the bottom of the walls in the hallway. (00:25:25)
Revealing mistake: After Selene bites Michael, Viktor picks him up and throws him through a wall. On the other side, he lands in a pool of water as do lumps of the wall, which float briefly before the shot ends. (01:43:55)
Revealing mistake: In the fight scene between Michael and Viktor, Viktor throws Michael in to a column and Michael lands face down. You can see his wire harness bulging under his pants. (01:47:15)
Revealing mistake: In the fight scene between Michael and Viktor, you can see several times where Michael's dark colored make-up has been wiped off his lips.
Revealing mistake: In the end fight scene between Viktor and the hybrid Michael, Viktor picks Michael up and throws him into a stone column. Terrible wirework then comes into play: Michael travels far too slowly towards the column for someone who was just thrown, he makes one perfect spin in the air on his way, and when he finally connects with the column, it's a delicate bounce off before the wire drops him on the ground. His legs don't even move from the "impact". (01:47:15)
Revealing mistake: After Selene jumps off the building at the beginning and lands, there is a very large upwards pull (that stays in place until the camera cuts away) in her cape near her head that is in fact the drop wire running under her cape to the harness on her back (although the wire has been edited out). (00:02:40)
Revealing mistake: When Lucian is draining blood from Michael, the tip of the syringe bends like rubber. (01:21:25)
Revealing mistake: As Lucien reprimands the Lycans for their pit fights, of the two Lycans who were just fighting and were naked during that fight, on the taller one the top seam of his underwear/pants is visible. (00:11:10)
Revealing mistake: The edges of Selene's bright blue contact lenses are VERY visible in the scene near the end where she is on the ground, talking to Viktor. (01:44:30)
Revealing mistake: At the end of the film when Viktor and Michael are fighting you can see Viktor pulling his punches. (01:47:35)
Chosen answer: In most of the shots, Lucien takes his coat off when he changes to wolf form, and the blade would be attatched to a mechanism in him coat. Also, the film gives us an example of the blade hurting a vampire: bloodloss. And that kind of weapon could do some serious damage, and as it probably wouldn't kill the vampires, it would almost definitely slow them down.