When the crew first pull up to Toretto's grocery store and see Brian, someone says "Nah, V, he ain't here for the food, dog" and "He's tryin' to get in Mia's pants, dog." It's pretty obvious nobody is saying those lines. They appear to have been added in later.
When the agents are debating whether Mia is clouding the opinion of Brian, the dialogue is, "Hey, I don't blame you. I get off on her surveillance photos too." But he is clearly dubbed over saying, "Hey, I don't blame you. I beat off to her surveillance photos too.
In the scene where Brian asks Mia for the number of Dom's cellphone to trace him, we can clearly hear the sound of a "clamshell phone" being closed, right after she gives the number to the Nextel operator. But in the next shot, Brian took the phone and continues the call.
Back at Dom's house after the first race. Just after Mia breaks Brian away from Vince, Leon says, "Aw, come on Mia, we were just about to get along", Jesse can then be heard adding "Yeah". However, his mouth does not move.
They call the police center to get a mobile phone location trace. She snaps the clamshell phone shut before handing it back, which would end the call - but he carries on talking with an open version of the clamshell in the next shot.
After the first race, it is acknowledged that Brian's Eclipse has blown its piston rings and requires the engine taking apart for repair, also some other kind of damage must have occurred (the manifold, according to his in-car laptop) that caused the floor-pan to fall through. This however doesn't affect Brian being able to evade the police and escape at a reasonable speed immediately after.
When Brian is racing the quarter-mile for the first time, the laptop on the passenger seat reads 'Danger to Manifold' and the foot plate on the passenger side comes loose and flies off. However, Brian then picks up Dom to evade the cops and Dom sits normally in the passenger seat. In actuality he would have nowhere to rest his feet and the hole in the floor would create a great deal of noise whilst driving.
When Brian and Dom first get to the party near the beginning of the movie, Dom hands Brian a drink, Brian immediately starts to clean the top with his shirt, a few seconds later we see him again start to clean the bottle.
During the race wars, when Jesse is up against Johnny Tran, we see Johnny Tran pull up in his car next to him and he is clearly wearing a buttoned up black shirt. However, once the ref lifts his hands and waves the signal to go, the next shot of Tran in the car and after the race shows him in a black tank top.
During the first hijacking when the car goes under the trailer there is only one trailer axle. When it goes to a wider angle shot, the trailer is back to having two axles. Also that trailer type has two support beams running down the center of the trailer from front to back. In this scene they are missing.
After leaving the parking garage where he has hidden his car, Dominick is spotted by a single police car and followed/chased. During the pursuit, the police car changes (as evidenced by the light bar on the top) between shots.
Toward the beginning of the movie when Brian drives into the alley and parks, there is a candy orange Honda Accord Wagon with no hood right next to the green Eclipse on the driver's side. After Hector introduces himself to Brian, he points across the alley to his car but we see the same Honda Accord that Brian is parked next to. You can tell by, 1) the headlights (Hector drives a mid-'90s model Civic hatchback which has more rounded headlights, but the car he point's to has rectangular Honda Accord headlights), and, 2) the design at the bottom of the windshield (both the car that Brian is standing next to and the car Hector points to have the same design, but later in the film, Hector drives to The Racer's Edge, and his Civic has nothing at the bottom of the windshield, also, note the headlights on the Civic and on the car he points to).
At the house party after Brian walks upstairs to use the bathroom, Vince approaches Dom and we see Dom already sitting down rubbing the top of his head. A few seconds later we see Dom sit down and start rubbing his head.
During the final heist after the trucker fires at Vince and misses, we see Dom reaching for him. The shot changes to a front view of Dom's Civic and Vince on the truck but the arm reaching out clearly has on a long sleeve black shirt where as Dom has on short sleeved white tee shirt which leaves his arm bare.
In the last race scene with the Supra on the LA streets chasing the dirtbikes during the day, the windshield is clearly cut out to eliminate glare in some shots, while in others, the entire windshield is present. The cutout takes the shape of the area covered by the wiper blades. In the same scene, the windshield is also visibly clean as well as visibly dirty.
When the boys pull up to the starting line at the first race, only three of them pull up and Brian over shots the starting line. The red car pulls up with the two boys. Yet when Brian over shots the line, the red car pulls up and stops again.
When Brian is driving up to Dom's store to get a tuna sandwich from Mia the Ford emblem on the grill of his red pickup is clearly missing. When he drives away after Dom tells him to leave, the Ford emblem appears.
When the officers are in the house and Brain pushes the detective. He is on the left side of the FBI agent. When they swap to show it from the other side, the agent falls past the FBI agent on his right side.
After the last truck hijacking and when Brian returns to Los Angeles, the Supra is constantly clean and dirty throughout the rest of the movie. But, when Brian pulls up to Dom before the last race, the car is very clean.
In Brian's first race, after Dominic speeds forward and his Eclipse is starting to swerve, the white car behind him doesn't seem to try to avoid hitting Brian's car, but is shown in the next shot of Dom and the other two racers crossing the finish line.
In the final truck robbery, Vince shoots a grappling hook through half of the truck's windscreen and pulls the glass out into the road. When it cuts back so he can shoot a second hook into the cabin, before he fires you can see the windscreen is intact. Then the grappling hook goes straight into the cab, and the windscreen disappears again.
During the last race, something in Dom's engine blows up. Yet it leaves smoke spewing out the back in some shots. When the two cars jump the track, in some shots the smoke is gone. Yet when Dom crashes the car at the very end, the car is seen smoking again.
Toward the beginning of the movie, Brian is pulled over by an unmarked black police car, a 1992 Ford Crown Victoria. When the stop is first being made, the Crown Victoria is a modified one that does not have a front grille with a blue Ford Oval on it. As Paul gets out of his car, the Crown Victoria is an unmodified one, with the grille and Ford oval on the front. So between shots, the police car changes.
When Dom is trying to rescue Vince from the truck, you can see a stuntman's arms driving the car in a few of the rear shots due to the long sleeve black shirt he is wearing compared to the short sleeve white shirt that Dom is wearing.
Although clearly done for cinematic purposes (to make it obvious what is in the truck), the container full of electronic equipment isn't packed at all realistically, with everything packed at the sides and none of it wrapped in plastic or on pallets. At the first turn, the boxes would be all over the place.
When Brian is testing the top speed of his Eclipse at the beginning of the film, he appears to have 7 forward gears. After seeing him shift into first before starting, you can count 6 more up-shifts after, either by seeing him change gear or by hearing it.
Right after the first race when Brian loses his car, Dom says "Granny shiftin' and not double clutching like you should." Double clutching takes precious time to do, time that you do not have during a drag race especially in a Mitsubishi Eclipse. The only time to double clutch that car would be in a road course race to save the brakes coming in fast into a corner.
In the last race when the Charger goes into the big wheelstand he is smoking the rear tires. This can not happen since smoking tires means the loss of traction and a wheelstand means no loss of traction.
The police scanner mounted on the dash on one of the "lookout" cars during the street race is an early-'80s Radio Shack Patrolman scanner which is not capable of receiving the current 800mhz digital trunking system currently used by L.A.P.D. and L.A. County Sheriff.
Johnny Tran isn't happy when he sees two empty engine bays, and suspects Ted of being responsible for selling the Nissan SR20 motors. The problem is that the cars in the shot are Hondas, and couldn't have been fitted with the SR20 engines due to the FWD-RWD difference.
When Brian is being interrogated by Dom and Vince after breaking into Hector's workshop, he says Hector has ordered a Motec System Exhaust for the three Civics. Motec is a manufacturer of engine management systems and data collection devices (electronics, basically). Motec does not make, and has never made exhaust systems.
The 1/4 mile race at the end takes the two "ten second" cars way more than 10 seconds to run. On top of that, in actuality, rail crossing bars lower long before the train is visible. If this was a ten second race, that means the rail bars dropped 2-3 seconds before the train appeared.
In the last scene of the movie, Dom tells Brian there is a quarter-mile from where that are to the railroad crossing. Approximately halfway in that race, the lights start blinking and the bars start coming down indicating the train is going to cross. They jump the crossing barely before the train crosses. If they are 10 second cars, that leaves only 5 seconds from the time the bars start coming down until they cross the tracks. Warning times for railroad crossings are much longer than that.
In the first scene of Brian in the eclipse he launches the car and only the front wheels spin during takeoff. In the big drag race the car lunges to one side which would only happen in the GSX all wheel drive model.
During the end race they show Dom shifting. At one point they show a floor shot with the gas and brake pedals. The brake pedal is wide, and in a manual Charger the pedal would be half the size in those years.
In The Fast and the Furious, on their date, Kia tells Brian that Dom and Letty met when Letty was 11 years old. In Fast and Furious 6, after their race, Dom tells Letty they met at her first street race when she was 15.
Why would Johnny Tran need to purchase stolen/gray-market engines? Cars that use the Nissan SR20 motor are sold legally in the North American Market, making the Nissan SR20 motor readily available at any Nissan dealership or even if he was referring to a Japan/Euro Market variant, he would've no trouble importing them instead of having to use a fence (Ted).
Towards the end of the film, when Brian and Mia are trying to stop Dom and co from robbing the armed trucker, Mia gives the Nextel operator Dom's cell number over Brian's cell phone. Since both Brian and Dom have active cell phones, why didn't they use one of them to call one of their friends when the Tran brothers blew up Brian's car after the first race?
Dominic tells Brian near the end of the film he needs to find Jesse before Tran and his gang finds him. But he clearly still has a bit of time left to pull off one heist, during which Jesse could have been in trouble already.
When Brian spins his Eclipse out while testing it in the stadium parking lot. You can clearly see that the reverse lights are on while the car is spinning. Indicating that they were doing reverse donuts to film the shot.
At the Race Wars when Jesse races the Honda S2000, the Jetta he is driving has drilled front rotors which do not have brake calipers on them. This suggests that the caliper is in fact a prop and simply stuck on.
In the alley when Dom and his crew arrive, the camera passes over the red RX-7. If you watch to the left of the screen, Leon's yellow Skyline comes flying in and screeches to a halt right before plowing into a car and some people. You can even see people move out of the way and a girl that was sitting on the car that was almost hit kicks her leg out of the way, as if trying to avoid getting hit.
After race wars, Brian returns to town and pulls his car into a driveway. His stuntman is clearly recognizable as the driver in this shot as his hairline is a good 2 or 3 inches further back than Paul Walker's.
In one aerial shot after the first race when the police are driving onto the street, you can see police cars waiting for their cues on the side streets. They have their parking lights on at first and then turn on their lights and light bars when they begin driving into the racer traffic.