Factual error: When Amy is fired from S'Nuff magazine she takes her story on Aaron Connors to Vanity Fair, who run with it. That is not going to happen. Amy wrote the article while a paid employee of S'Nuff magazine and that means the copyright in the article (and, very relevant to this issue, the photographs of Aaron they paid to have taken), resides with them, not with her. It isn't hers to sell. No magazine editor of any standing is going to buy an unsolicited article without checking its provenance backwards and forwards, and that would mean checking with Amy's previous employers - after all, what would happen if they changed their minds and ran the story themselves?
Revealing mistake: Gracie hugs the Russian waitress in order to have a better view of the disc hand-off appear on the monitor. As she raises her left hand that holds the book/camera lens, we see that the digital feed that appears on the monitor stays steady and level, even though she is raising the book/camera lens higher and closer to her face. Obviously the feed that we see on the monitor is not taken from the book/camera lens. (00:04:10)Super Grover
Continuity mistake: In the beginning of the movie he is not taken onto the hockey team. After he is hustling at the driving range he goes to toughen up. As he is toughening up, Chubbs unplugs the machine. The kid tries it, but he never plugged it back in and the machine still manages to work. (00:15:10)
Other mistake: In the scene where the kids are shooting arrows and the coach gets hit by one, they send a girl to call 911. If you look closely and follow her in the background, after she runs a few yards, she slows down and eventually stops and stands there playing with her hair. Talk about help... (00:57:05)
Deliberate mistake: When MIB agents exit the lift to get into the main hall of the MIB Office, the lift opens halfway up the wall and they need to go down a little platform. But when K and J return during the lockdown and face the trashcan with guns, the lift opens at floor level, so it can be conveniently peppered with bullets. (01:02:05)
Factual error: At the very end of the film Bruce is reporting on a drive for blood donors, and Grace leads him over to the booth to give blood himself - he is even wearing a tourniquet. However, he is supporting himself on a walking stick - he is not fully recovered from the injuries he received when he was run over, which happened when he was hit by a moving car - injuries which left him clinically dead. There is absolutely no way that a person who has suffered life threatening injuries and has undergone the (inevitably) intensive drug therapies and surgical procedures involved while under treatment in hospital in the fairly recent past would be allowed to give blood. There is no way that the Red Cross (or the US equivalent) would want to encourage people who have recently been hospitalised to try to give blood. Not only would that be the height of irresponsibility, they would be wasting precious resources and staff time turning away people who would not be allowed to give blood.
Continuity mistake: Agatha's nightgown strap switches between hanging down on her arm, or being up on her shoulder, normally.
Revealing mistake: On Billy's first day of school when he is outside waiting for the bus and it just passes him you hear the noise of kids on a bus, but when it passes no one is in it.
Factual error: Basic physics - Hancock throws Michel from a dead stop to above cloud level in about eleven seconds. The clouds are bog standard cumulus which form at around 7,000 metres in temperate zones. This means that Michel accelerates to about 700 metres per second instantly, from a dead stop. Obviously he cannot accelerate during his ascent, so his starting speed has to be at least that. (In fact he would have to start his ascent much, much faster than 700 metres per second as he would be constantly decelerating due to gravity and air resistance, but it will do as a start point.) Michel accelerates from 0 to 2,520 kilometres per hour - twice the speed of sound - in zero seconds. He would be accelerating at around 5000 Gs, turning him into a very long streak of fine, pink mist.
Other mistake: In the beginning of the movie, when you first see Mary-Kate (aka Mel) and Ashley (aka Ally), Mary-Kate walks off without ever closing her locker.
Revealing mistake: Near the middle of the movie Samantha Mathis is walking across the high school campus. The name of the high school in the movie is "Hubert Humphrey High School, " but behind her, above the library door, a sign says "Saugus High School Library". Shows better in 4.3 aspect. (00:31:45)