When Jane and Angela are outside talking to Ricky at school, Angela's cigarette keeps growing and shrinking throughout the conversation.
When Colonel Fitts breaks into Ricky's room in a rage and punches him, the blood is already on Ricky's nose before the fist makes contact.
After Lester removes Angela's pants, he moves his hands along her body and she is wearing her pants around her knees.
After Ricky Fitts's father has beaten him up for opening the cabinet containing his Nazi plate, he has no evidence of any facial scarring that would have been the result of the open wounds caused by the attack.
When Carolyn (with a squeegee) is outside cleaning the sliding glass patio doors opening out onto the pool for the open house, a sheer curtain panel is visible inside. But when she throws open the front doors to the open house and welcomes prospective buyers, in the background the sheers are flanked by heavy plaid curtains drawn open to either side. After she fails to sell the house and closes up the patio door at the end of the (same) day, the curtains and sheers have disappeared and she draws textured vertical blinds closed across the same glass doors.
In the dinner scene where Lester throws the bowl of asparagus against the wall, the picture frame has been centered between the windows over the console table, and the table lamp visible in an earlier scene has been removed. These changes are not down to continuity as such. The script originally called for Lester to throw the plate on the floor; however, it was decided that he throw it against the wall instead without the knowledge of Annette Bening or Thora Birch. It had to be done in one take (which it was) to get a real shock reaction. The lamp was removed to avoid any debris knocking it over, and the picture was repositioned in line with Lester's aim for a clean throw and to minimize any risk of Kevin Spacey knocking the picture off the wall, spoiling the 'one-take shot'.
When Angela and Jane are outside the school talking to Ricky, there is a shot in which the filter of Angela's cigarette is visible, and it's clearly white. As the cigarette is half-smoked, it should be brown from the tar. However, this could be deliberate as it could be that Angela and Jane are not really smoking and just trying to look cool.
The plastic bag video was supposedly filmed with a hand-held camera but there is no hand shake. However, Ricky stated that this video is his favorite and acts like he is very proud of filming it, so it would make sense that his favorite "masterpiece" would be of better quality than most other videos and without any visible camera shaking.
In Jane's phone book, she has Lester's work phone number as 555-1251; he gives it as 555-0199, but he may have multiple lines. However, this is not her mother's work number of 555-0195, despite some reports to the contrary.
Ricky takes out the cup of urine and explains to Lester that he needs clean urine to pass a drug test at home. The test obviously does not require the urine to be "fresh", so why doesn't Ricky just keep his own urine around from when he has not used drugs?
Cannabis can be detected in the urine of regular users (such as Ricky) for up to 90 days after consumption. It is very likely that there has never been a period during which Ricky's urine had no detectable traces of cannabis (considering his frequent use), and even if there was, it would be too complicated for Ricky to figure out when exactly his own urine can pass the drug test.
While Carolyn is driving home from shooting practice, she turns the wheel quite sharply several times but the scenery never turns with her.
When Ricky opens his father's glass case to remove the Nazi plate, there is no glass in the door.
After Carolyn and Buddy order takeout in Mr. Smiley's drive-thru (Lester hears them ordering inside on a speaker), they then drive past the menu board with the intercom/speaker for placing orders (Lester was shown ordering here in an earlier scene).
Lester driving to the song "American Woman" appears to be making a continuous right turn by the tilt of his steering while driving down a straight road (compare the position of the steering wheel in the next scene where he is actually driving the car into Mr. Smiley's). The Camry is obviously being towed on a process trailer for this shot but someone has neglected to straighten out the front wheels of the car before turning the engine off and securing it to the trailer.
When Lester and Carolyn are at the party and walking up to talk to Buddy, Lester can be seen at the bottom left looking directly into the camera for a split second.
When Jane is being filmed and talking about having her father killed (jokingly), she is smoking pot in the room. The room is Ricky's and it is known by this part of the movie that Colonel Fitts hates pot smoking. This is literally the scene where Ricky explains that his dad caught him smoking pot when he was younger and sent him to military school or something along those lines. It doesn't make sense for them to be smoking weed inside the room.
When Ricky begins recording Jane, the camera makes the sound of ejecting the tape.
When Carolyn slaps Jane in the face, Carolyn can be seen yelling at Jane, from behind, even though the soundtrack is silent.
At the beginning of the movie, when Lester is in the shower, you can see a reflection/silhouette on the shower door.
After he is beaten by his father for looking at the Nazi plate, Ricky Fitts looks in the mirror to examine his wounds. The edge of the camera is visible in the mirror for about a second, then the frame is rearranged so it is no longer visible.
When Lester is driving in his car after leaving his advertising job, the trailing motorcycle cop escorting the picture vehicle (the Camry) being towed on the process trailer behind the camera car can be seen going in and out of the shot in the rear window.
In the opening sequence of the film, in the overhead shot of the Burnhams' master bedroom, Lester is lying in bed on his stomach, rousing when his alarm clock goes off. Circular white matte board cutouts cap the top of the lampshades on either side of the bed, blocking the bare light bulbs from shining straight into the camera lens (and probably hiding color-correcting gels on the bulbs that would only be found in lamps on nightstands in bedrooms on stage).
Toward the end of Ricky's and Jane's first kiss in his bedroom, the moving shadow of a crew member or piece of equipment can be seen at the bottom of the window and blinds projected on the wall (to the left of the black floor lamp, behind Ricky, far left edge of frame).
When Lester is singing "American Woman" in his car, buildings from Burbank, California, (including the building bearing "The Disney Channel" logo at the time) are clearly seen in the reflection of his windshield. The telephone area codes and newspapers set the film in the Chicago area.
During the basketball game, a player on the home team (#11) commits a traveling violation by taking three or four steps without dribbling. Even though it looks like a cut-and-dry call, none of the referees stop the game.
During Lester's weight training, he's doing a close-grip bench press. This is an "isolation" exercise that wouldn't be done by a novice.