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)
Continuity mistake: When Gregory reveals himself as the killer, pay attention as he walks towards Tree clapping. The mask on the ground behind him is initially face-down and right next to the wall. But a few shots later, suddenly it is face-up and has moved about a foot to the left.
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 amount of snow cover on the lake is inconsistent. There is solid ice with a foot or more of snow cover when Grace goes out to ice-skate, but once she is on the lake going toward Mia by the fishing hole, there appears to be only a couple inches of snow cover. However, when Richard is skating toward the fishing hole to rescue Grace, he falls into several inches of snow. The thickness of the ice around the fishing hole also varies. (00:29:15 - 00:31:10)
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)
Continuity mistake: Scooby and Shaggy are lying face down on the massage table when the zombies arrive. Shaggy has his robe lowered baring the upper back, but in the close-ups you can still see the robe up covering his shoulders perfectly. (00:28:00)