Revealing mistake: The structure/set-up of Richard's house (front view) doesn't make sense and can't be real. The half of the house to the right of the screen is at an awkward angle and has no windows. What little of the roof that can be seen is flat - not conducive to snowy Massachusetts. The bottom of the door to the right of the garage door is inches above the driveway pavement (elevated with no step). The deck wall to the right of the yellow door is higher than the door but the front rails only reach halfway. (00:03:25)
Revealing mistake: The cement block section of the house by the front door that Greg was painting "changed" to a flat board for a short time and then went back to the blocks. (01:05:28)
Revealing mistake: In Guatemala, when Arnie shoots John, in the shots from behind Arnie's body double is noticeable.
Revealing mistake: The way the outside steps were constructed - a series of perpendicular boards with no side support - would not be able to hold weight. They would easily collapse under pressure. (00:38:53)
Revealing mistake: When Shin begins chopping off Jay's head, in the close-up shot a line can be seen around the part of Jay's neck that hasn't been cut yet, revealing that it is a prop head. (01:35:05)
Revealing mistake: The camera holds on a close-up of the article featuring the 'Female President of the Network' Caroline Morton for 3-4 seconds, long enough to allow to quickly browse the text and easily see that it's a generic article about women in workplaces used as filler text and not the interview Katherine is reading. (00:03:25)
Revealing mistake: After most of the people trying to hang onto other people holding onto the ascending helicopter fell off, a downward view from the helicopter showed a man effortlessly hanging onto the landing skid and a woman just as effortlessly grasping his jacket's shoulder. (00:02:50)
Revealing mistake: When Anita goes to destroy their getaway car you see her pour gasoline all over the roof and hood. Then when she lights it on fire it's only burning inside the car. (01:06:40)
Revealing mistake: When they're playing kickball the first time (when Phil sucks at it), the shots change from either the sun rising/setting to fog and cloud cover.
Revealing mistake: When Nathan and Theresa are talking on the front porch, the background is fake (and mostly blurred). The white picket fence just doesn't look real. A hanging plant on the porch sways a little from wind but the two nearby trees (leaves/branches) are stationary. Next, one tree gets a gust of wind while the other one does not and the remaining trees in the background do not show any movement. (00:13:50)
Revealing mistake: The use of a green screen (or other color) during most of the cafeteria scene is obvious if you watch the people in the background instead of the main characters and is flawed in a few ways (e.g, varying angles, greater distance, continuity of a person, etc). For example there is a man wearing a blue shirt/tan pants and carrying a briefcase walking down the aisle toward the Good Boys' table. When the man is walking along the wall that is behind the Good Boys, he is further ahead than he is when he is picked up again. Also, this man shows up in front of Max when Max is walking to Soren's table. The man also appears walking along the back wall with a woman. Watching the wall behind Thor and Lucas, it is sometimes at an angle and other times looks more distant. Some of the people would essentially be walking "out of the wall" in order to appear where they do (e.g, the boy with a backpack).
Revealing mistake: Numerous time in the film the animals walk from shade into sunlight without their eyes reacting.