Revealing mistake: When Alana is walking toward the students, the hedges are mostly dark green, sheared level across the top, and reach to her elbows. Later (after Gary tells Alana he will take a mirror), the hedges turn mostly yellow and flower-like across the top, are quite uneven, and are as high as her shoulders in spots. (Use of a green screen is apparent). (00:00:40 - 00:01:26)
Suggested correction: One look at the scene make it apparent this entry is totally incorrect. The bushes look natural. The yellowness is just colour grading. There is no sign of green screen usage whatsoever. It would make no sense for this film, especially if you realise that director PT Anderson is known to be very much against the use of any sort of VFX or green screening.
Revealing mistake: Ronnie is shown looking through the vertical-rectangular window of a brown door to Joey's hospital room. His eyes are angled to his left, indicating he is looking toward the person in bed to the left of a double room. When Ronnie is standing next to and facing the man in that bed, there's no door with a window behind him that he could have been looking through. There is a windowless white door on an adjacent wall. (00:00:40 - 00:03:42)
Revealing mistake: Lower-third shots of the aquarium in the background at the Delaware Raceway's sports lounge were often blurred and did not look like they matched full views of the aquarium. (00:36:05 - 00:36:34)
Revealing mistake: DEA Agent Rick Bowden was already seated "in the best position" before knowing where Ross would sit in the SF library. Chris Tarbell already had a surveillance camera behind the seat Ross chose, giving him a clear view of Ross, also before knowing where Ross was going to sit. Even if there were cameras in other positions, the DEA Agent and Chris Tarbell being at the right spots in advance was too coincidental to be by chance alone. (00:02:09 - 00:02:30)
Revealing mistake: After Charlie talks to Emma in Francine's old bedroom and is standing in the doorway, the background (segment of the hallway) is obviously fake. Shown are less than five of the top steps on the staircase, only a fraction of the size of real steps. The lower section of the banister is also a reduced size. (01:31:35)