Plot hole: The FBI agent (played by Vince Vaughn) goes into the serial killer's head to save Jennifer Lopez. When he's in there he sees the tank with the water nymph. On the tank are strange symbols which provide the FBI with the clue needed to find the latest victim. Makes sense so far. But, go back to the scene just after the FBI have captured the comatose killer and are looking in his basement. The FBI are looking at the contraption that the killer uses to suspend himself over the victim. On the contraption is the same symbol seen later on the water nymph's tank. Why didn't the FBI follow up the symbol then? In fact, why didn't they try to find out where the hell he got the contraption in the first place? Doing either of these things would lead them to the information on the whereabouts of the latest victim. There was never any need for Jennifer to go into the head of the killer at all. Which makes the whole point of the movie irrelevant!
