Other mistake: When Joe shoots the boy at the back of the house, he walks to the front at the same time a woman a few feet away walks toward him with a pram, and there are people in the background. There is no reaction from anyone to the obviously loud gun shot noise - his gun did not have a silencer on it.
Other mistake: When Will is in the club and Lucia's friend is checking his wound she feels around to see if the bullet is still inside his body. She says the bullet is not there so cauterises the wound. Will does not have an exit wound so the bullet must, therefore, still be inside.
Other mistake: Throughout the saga, blood has been shown as essential for vampire's healing factor, and Selene herself used her blood to heal people. Somehow, this time around neither her or her pal David think in any way of this basic fact, making a complicated trip to the vampire doctor necessary, who simply feeds the vampire kid some blood, the very first thing any vampire would do to regain strength.
Other mistake: When Steve, wearing his improvised shark cage, heads underwater to turn off a relay to prevent the others from being electrocuted by a falling wire, he is shown breathing through a snorkel taped to several metres of hose, open at the surface end. In reality, human lungs can't expand enough to pull fresh air through more than a couple of feet of hose. That's why diving hookahs use an air pump to feed air from the surface to the regulator mouthpiece.