Other mistake: Vanessa is illiterate, but easily reads the Hi-Way Café menu. (00:48:35)
Revealing mistake: At the end of the film Vanessa gets crazy because Bob kills her grandma, and she starts beating him up in the caravan, hitting him and throwing various stuff at him. Throughout the scene, Reese Witherspoon's' stunt double is really obvious. Her hair looks completely different!!!
Continuity mistake: When Bob and Vanessa are eating in a diner, Bob says "Yes, it's a form of senility," and a tissue which was sitting beside a plate vanishes in this shot. (00:28:20)
Continuity mistake: When Vanessa hits Bob with a plant, Bob's pink hairnet is off. It's back on in the next shot. (01:31:55)
Continuity mistake: When the girls are sitting in the plastic chairs watching the TV in the jail hall, in one shot Mesquita bends down and leans against the only empty plastic chair. Then in the following shot she's not there. (01:08:20)
Continuity mistake: When Mrs. Sheets pulls up outside the motel where the Lutz's are, her front passenger door window is rolled halfway down. Then later when Vanessa steals the car, the window is fully rolled down. (00:15:00 - 00:17:30)
Continuity mistake: When Vanessa is walking down the path to her grandma's caravan, her shadow changes from extremely long to very short between shots. (01:29:15)
Revealing mistake: In the fight scene at the end, Vanessa is hitting Bob, and Bob has a gun. However he repeatedly fires it over and over without reloading. (01:31:40)
Continuity mistake: When Bob climbs out of the car, running away from Vanessa he runs in a straight path from the drivers seat, very far away from the van and is then shot by Vanessa. Moments later when Vanessa robs him, he is closer to the van and near the rear of it. He is in a different location and his body has also rotated. (00:46:15)
Revealing mistake: When Bob and Vanessa are battling at the end of the film, he fires 22 shots before he dies. Besides the obvious fact that the gun doesn't hold that many bullets and wasn't reloaded, there was no sparks or smoke from the gun on almost all of the shots and although he seemed to be firing randomly around the room, there are no holes in the walls or even in window like there should have been, especially seeing as a couple of shots made it outside to the policemen.
Audio problem: When Bob runs from Vanessa, out of the car after being shot, Vanessa shoots her gun, and we see the bullet hit the floor, with the audio of gunfire to match it. Then audibly we hear Vanessa shot the gun two more times, however visibly three bullet-holes appear in Bob's brown coat, so they forgot the audio for one of the bullet-fire, also revealing that Bob was probably wearing squibs.
Continuity mistake: In the car when they are driving, Bob slices off Vanessa's entire ponytail; it remains short afterwards during her interview with the two policeman but then in the courtroom when she meets Bob again, she has her hair in a reasonably long ponytail.
Continuity mistake: When the social worker pulls up, there is no christmas-tree air-freshener hanging from her mirror. When Vanessa nicks the car, there's a christmas-tree air-freshener hanging from the little black windshield mirror.
Visible crew/equipment: After the detectives find Wolverton's shed load of porno, it cuts to Detective Mike Breer speaking on the phone in the kitchen. As he walks around the counter, a red boom mic is visible, following him. (01:23:10)
Visible crew/equipment: When Vanessa enters the Hi-Way Café, as the glass door closes behind her, the reflection of a boom operator holding up a long boom pole is perfectly visible (00:48:20)
Continuity mistake: Brooke Shields runs to shoot herself in the bathroom, and the bathroom door is hinged on the left side of the door frame. The two detectives enter the bathroom and the door is now hinged on the right side of the it. (01:23:55)
Visible crew/equipment: When the camera first pans across the blackboard with the sentence "The cat drinks milk" on it, there is a perfect shadow of a boom mic cast above the sentence. (00:02:50)
Other mistake: At the end when Vanessa is sitting in the deckchair outside her Grandmother's caravan, she asks the cops if they have a cigarette. The view cuts to the cops who smile at her and chuckle; when the view cuts back to her, she grins and you can see a faint plume of smoke rising from below the camera, indicating she already has a lit cigarette. She didn't light one at any point either.
Revealing mistake: In the shot of Vanessa's dead grandma, her closed eyes flutter and her tounge moves. (01:31:20)
Continuity mistake: When the contents of Ramona's handbag are spilled out onto the car bonnet by the policemen, the items' positions differ between shots. (00:09:50)
Answer: Even experts in a given field occasionally like to consult a text on the subject.