Revealing mistake: When the black cat was going up the staircase and got to the first landing, it turned its head to look directly at the camera, then continued climbing the staircase. (00:08:13)
Revealing mistake: When the door is kicked in, it does not sound very loud or like a typical door smashing. An interior view shows the door is about half the width of a standard door and a 3-4' board can be seen falling vertically along the door frame/ wall (then disappears). Instead of hearing someone kicking open a door, the sound more accurately matches what happened: a thin door breaking through a board holding it closed! The "breaking in" scene also has some "stupidities." Stewart (without first trying to see if the door was not locked) uses a cordless drill on the door's lock and a second man then uses his right leg to kick it in (without first seeing if the drill unlocked the door). A third man brought a crowbar, which could have easily eliminated the need for someone to bring a drill or for one of the men to risk a foot/ leg injury by kicking open a door. (00:02:11)
Revealing mistake: It looked like Theo's gold and white checked shoes were a few sizes too big and wide to make it easier and quicker for Laura to put them on her, but Laura still had some difficulty slipping on Theo's oversized shoes. The material even folded down around the ankle when Laura was putting on Theo's right shoe. (00:03:42)
Revealing mistake: When the shop teacher walks up to Millie at the start of the film and slams the book, as he begins to step in front of her table, you can see him subtly "step down" even though he's on an even floor. Due to technical limitations, there needed to be a raised surface on the floor for the camera, a few inches off the ground. It was painted out digitally, but you can still see the actor step off the platform, making it look like he's "stepping down" on even ground. (Confirmed in Blu-Ray commentary.)
Revealing mistake: Although it appears that Edgar (and later Norman) put his eye up to the hole in the wall to look into the opposite room, the eye is obviously fake. Too much of the sclera (white part of the eye) is showing and the upper eyelid is too far above it; the upper eyelid typically reaches or partially covers the top of the iris (colored part of the eye). Also, the eyelashes go downward instead of being curved upward. (00:18:05 - 00:19:49)
Revealing mistake: Grandpa holds the can of soda/ pop at about a 45° angle when he is going to pull the tab. Robert De Niro, playing Grandpa, is placing the can in the position needed for the carbonated contents to spray all over his face. (01:13:05)
Revealing mistake: In one of the scenes in the ballroom you can see that the thumb claw of the head witch is put on top of her real thumb.
Revealing mistake: The backgrounds during the pawn shop scenes often change, suggesting the use of a "green screen." For example, the grandfather clock was behind the clerk to his left, then not there, but back again. Sometimes shirts are hanging in the front windows but other times there are other items there. (00:47:57)
Revealing mistake: After the kids take their seats at the game, the people behind them change, indicating the use of a green screen. (00:13:00)
Revealing mistake: When Cecilia is lifting an iPhone up to her ear, it starts ringing as if she's making a call. But on the screen, you can very easily tell it doesn't say "dialing" or "calling" - it's a timer showing how long the call has been going on. She was already on a call before pretend-calling. (01:42:47)
Revealing mistake: When Maya Rudolph and Tim Meadows are in their car at the drive-in theatre, whilst Maya Rudolph says "We got Hubie Dubois spying on everybody", there is a close-up shot of the wing mirror with Hubie's car reflected in it, along with several other cars and a building in the background also reflected. Despite being a reflection, any text or numbers reflected in the mirror are not reversed. The number plate on Hubie's car is spelled out forwards, and the sign "Salem Drive In" on the building in the background is spelled forwards also, and not reversed as they normally would be in a reflection. (00:49:17)
Revealing mistake: The location of and distance between windows on the mobile home should stay the same, but do not. The home's exterior is constructed of vertical boards/slats, which can be used to make a rough estimate of the number (then distance). Initially, there were about 24 vertical boards between the shortest window and the window to its right (on-screen). When David and Anne were close to the house, there were a lot more boards between these windows - closer to 36+. The mobile home was "fabricated". (00:02:18)
Revealing mistake: Throughout the movie, there are mixtures of real snowfall and artificial flakes. When John is at Paul Carnury's house, in particular, the "fake" snow is quite apparent. John could be standing outside in the snowstorm yet little or no snow hit his jacket. (At one point, a few flakes land on top of his head.) When John breaks through the front door, a gush of "flakes" come inside and the ones on the back of his jacket fly and/or roll over his body. "Snow" even bounces upwards off his jacket. (01:13:34)
Revealing mistake: The green screened scene behind the ticket collector on the dock isn't moving. The waves on the water are paused, then the background is moving again in the next scene. (00:08:00)
Revealing mistake: Near the beginning of the movie, there does not appear to be a curtain (or window) on the left side of the screen (e.g, when Samantha is sitting on the couch), but there is near the end when Chloe enters the now-empty room. The use of a green screen seemed apparent throughout the movie. (00:04:19 - 01:23:04)