Plot hole: Peter goes into Carl's mind to save Catherine. 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?
Continuity mistake: When Carl is washing plates, he has a pile of clean ones stacked on the counter. He places a third one down onto the pile but when we see the pile there's only two, then suddenly three, without him placing another one down. However when the plate he cleans falls and smashes, there's just two in the pile again.
Continuity mistake: Just after Peter has entered Carl's mind for the first time, it then cuts to Julie who is trapped in the water tank. The sprinkler turns on and she gets up - her blue shirt tightly tucked into her skirt. It cuts and suddenly all of the shirt is hanging out. In these same two shots, the sleeves on the shirt alternate from normal to suddenly rolled all the way up her arms.
Continuity mistake: When Julia is trying to figure a way out the cell, she starting feeling around the edges of the glass panels etc., and she then comes to the end and stands by the green bench which is at the side of the cell. Julia's black heels sit on the bench, but then when Julia notices the pipe and climbs up to attempt to pull it, in the overhead shot her black heels have vanished from the bench.
Continuity mistake: When Julia is trying to figure a way out the cell, she starting feeling around the edges of the glass panels etc., and the ring that she wears on her left hand goes from only showing the gold band, to suddenly rotating to revealing the stone, between shots when she grabs the pipe.
Visible crew/equipment: In one scene Julia is in the cell and the sprinkler turns on. It stops, then she goes to the glass panel and starts banging on it and yells "Let me the fuck out! Let me out!", and you can see the reflection of a cameraman with a camera trying to keep a low profile, as she runs across, banging and shouting this.
Continuity mistake: When Catherine enters Carl's mind for the second time, she follows young Carl into the house, and he is doing the dishes. The large plate in his hand does not have any designs on it, however, when they show him putting the plate down on the counter, the plate has a flowery design. The plate already on the counter (which he puts the other plate on) has a flowery design on it, but between these same shots, the design on the plate totally changes.
Continuity mistake: As we see Carl in the dreamworld talking about how the dead woman in the tub was his "first one" and how he "made such a mess," the woman's breasts were visible almost to the point of a "nipple slip." The third shot in which we see her, doesn't even reveal any cleavage. Her head and arms are also in a noticeably different pose, too.
Continuity mistake: In the scene where Carl is in the bathtub before being caught, there is a red razor and bar of soap on the edge of the tub next to his right shoulder. In the next camera shot when he goes to get out of the tub, the razor is already on the floor before he even hits into it.