Revealing mistake: When Selene falls into the tunnels of Tanis's lair where the lycans are, you can see the pad she lands on. It's almost passed off as falling snow, but watch how as she lands the 'ground' squeezes like a pillow. This was pointed out in the director's commentary. (00:44:00)
Revealing mistake: During the final battle with William, Selene throws 2 explosives into the roof. The resulting explosion sends debris hurling towards the ground and the water, the rocks however float in the water.
Revealing mistake: As Selene and Michael infiltrate Tanis's lair of exile, Selene kills both of Tanis's vampire girlfriends. Afterwards, as Tanis is carrying one of the dead girls' body to a dungeon we can plainly see the girl's arm holding onto his shoulders/back of his neck. If she was dead, her arm should have simply hung somewhere - not draped around his shoulders, obviously holding on like she is.
Answer: Yellow brick road - Elton John.