Plot hole: At the end of the movie where David and his friends are attempting to break into Steve's house, David has the door code and attempts to gain access once by using it. Steve then tells his wife and the kids to go hide upstairs and turn off all the lights so nobody will know where they are. Then Steve and his wife go to another part of the house, away from the front door. Then, we hear David and his friends using axes and a big log to try and break down the door, "before* Steve secures the door with household appliances later on. Why wouldn't David have just kept trying the code?
Other mistake: In the scene where Nicole opens her locker and a note from David falls out, the handwriting is exactly the same as the seen where Nicole leaves a note taped to the bedroom door for her father. Although the letters are larger, the same applies to the note on the father's vandalized car, which says he's popped both of their cherries.
Continuity mistake: Near the end of the movie, when Mark has the mother and father bound and gagged, the mothers tape gag slips off and is magically resealed several times.
Continuity mistake: There is a change of scene from an inside shot to an outside shot in the first hour of the movie. There is an extremely obvious skip in the film where it was edited.
Continuity mistake: When David talks to Nicole in her Jeep, at one point her hair is over her shoulders. Then they show David again then back to Nicole and the hair is behind her shoulder and it keeps repeating through out the scene.
Continuity mistake: At the end scene when Mark Wahlberg and his friend are attacking the girls in the bedroom, keep an eye on Reese Witherspoon's left shoulder. Her shirt repeatedly changes from torn and her bra strap showing to being intact and the strap covered up quite a few times within the scene.
Other mistake: In the scene where Gary and Nicole are leaving school and Nicole is telling Gary "please don't tell Margo'' when we first see them they are wearing clothes that were worn in the ending then it switches. Keep eyes on Nicole at first her clothes is the black dress with pink shirt underneath and her hair is down, it switches and she's wearing red pants, purple shirt, and hair in a pony tail.
Continuity mistake: David tells Nicole that her dad hit him in the chest and left bruises. But later in the film when David is carving on his chest, there are no bruises.
Continuity mistake: The wound on David's back from being stabbed by the peace pipe at the end changes drastically. When we first see it, it is a very bloody wound on his upper back near his shoulders and head, but when we see it in the next shot, not only is it smaller and less bloody, but it also changes position to being further down in the middle of his back. (01:30:45)
Continuity mistake: David throws Nicole in her pool yet in the next scene when he kisses her, her hair is dry.