Continuity mistake: There wasn't much blood noticeable on the axe after it was used to chop off the mermaid's tail, but a little later when the man was carrying it over his shoulder, it was heavily covered in blood and dripping. (00:14:17)
Continuity mistake: For a second time in the movie, someone buzzes June on the intercom. She tries to overcome her fears and get out of the apartment, but can't. She shuts the door, leans with the left hand on the doorframe by the chain, and lowers her arm. In the next shot, Naomi Watts is breathing deeply still with her hand by the chain. (00:06:05)
Continuity mistake: In the prologue, the Nazis storm the Bresson residence. The elder Professor Bresson is sitting at his desk, back turned to them. There's an open fountain pen next to him, right by a paper sheet, but when Bresson answers rather defiantly to the bad guys, the paper sheet suddenly has disappeared. (00:02:15)
Revealing mistake: Obvious use of green screen for buildings across the street. On and off, the background fades, and buildings appear higher or lower depending on the camera's angle. At one point, the angle of walls behind Rex (Bruce Willis) is at a downward angle, and his head is almost touching the ceiling. (00:06:10 - 00:07:25)
Other mistake: The Burglar (while tied to a chair and talking about "My Darling Clementine") says, "Apex of Ford's art, you feel me?" Vikar (James Franco) responds, "I feel you." The movie starts in 1969, but rapper E-40 (Earl Tyrone Stevens, Sr.) - "slang master" - supposedly created the expression "you feel me" in the early 1990s. (00:19:53)
Continuity mistake: The location and intensity of Lavinia's purple hair highlights vary throughout the movie. For example, the purple highlights on the right side were far more pronounced (two wide, distinct, vivid lines) when she got home compared to when she first met Ward. Lavinia rode her horse Comet home, so her hair would have been wind-blown and the highlights would not have been likely to be neatly straight down, especially since she has long curly hair. (00:05:10 - 00:07:13)
Deliberate mistake: Carson's [John Travolta] cat Raymond did not appear to be in the pet carrier when he was running out of the building to his car or when walking to his office and placing the carrier on the desk. (00:02:15 - 00:03:30)