While showing the monitoring equipment, Hank tells Fred that he could be anyone from Arctor's circle of friends, including Barris. This made sense in the book, however, by this time in the movie Hank has already seen Fred alongside Barris, so he could not possibly think they are the same person.
(at around 10 mins) When Barris is served in the diner, french fries are scattered over his plate. When seen again, the french fries are replaced with vegetable sides.
(at around 20 mins) When Ernie lifts the bike, he picks it up by the top wheel. When he is shown carrying the bike a second later, he is holding it by the lower bar.
When Bob wakes up and reaches over Connie, he is wearing blue boxer shorts. But in the footage that he watches later, he is naked.
Donna's earrings disappear and reappear while she is drinking coffee in the restaurant.
(at around 10 mins) Arctor's residence, on the computer screen, is shown as Anahiem, California, a misspelling of Anaheim. The associated zip code, 98345 is for Keyport, Washington.
(at around 35 mins) After the car breaks down on the freeway, they cut to a scene where the car is facing backwards on a flatbed tow truck. If the car was picked up on the freeway, it would be facing forward unless the tow truck picked up the car from the rear which on the freeway would be highly unlikely.
Donna's car is a convertible, but whenever she's having a ride with Bob (at relatively high speeds), their hair is barely moving.
(at around 35 mins) During the conversation in the tow truck between Barris and Arctor, visible landmarks switch between Irvine, CA (on the Tustin border) when the camera is on Barris, and Orange, CA (on the border of Anaheim) when the camera is on Arctor. In addition, the same exterior shots from Interstate 5 of the Irvine Technology Center business park are passed several times in the same scene.
The group knows (and she says it herself) that Donna doesn't like to be touched because of her drug usage. Though, when she's in the house after the guys get back with the towed car, she sits on the sofa with Robert and grabs his arm and places it around her. Later, she rejects him when he says he wants to hold her in the same way, saying that she does a lot of coke and she has to be really careful.