Other mistake: After the first race, in the scene where Lightning is rushing out on the stage thinking he is the winner, loads of confetti is shot out when the King and Chick Hicks gets onto the stage. The confetti is then falling down, but not a single flake hits any of the cars. However, in the following shots, you can see plenty of it on the stage underneath the cars, even though they haven't moved.
Continuity mistake: In the tractor tipping scene, Mater demonstrates to McQueen how to do it using two tractors before Mcqueen's first try. And then when McQueen accelerates to make the noise and we have a wide open shot of the field, we can see that all the tractors in the field are still turning. Missing are the two already done by Mater.
Deliberate mistake: During the very last race, Lightning McQueen gets next to the green car, and the reflection of that green car's chrome "C" emblem is seen on Lightning McQueen's hood. However, the C is facing the right way. Since the C is placed on the green car in the correct direction, the reflection on Lighting McQueen should be a mirror image.
Dusty Rust-eze: Thanks to you, Lightning, we had a banner year!
Rusty Rust-eze: I mean, we might even clear enough to buy you some headlights!
Dusty Rust-eze: Are you saying he doesn't have headlights?
Rusty Rust-eze: That's what I'm tellin' ya - it's just stickers!
Lightning McQueen: Well, you know, race cars don't need headlights, because the track is always lit.
Dusty Rust-eze: Well, so is my brother, but he still needs headlights!
Lightning McQueen: Look, Doc said when I finish, I could go. That was the deal.
Doc Hudson: The deal was you fix the road, not make it worse. Now, scrape it off! Start over again.
Lightning McQueen: Hey. Look, grandpa, I'm not a bulldozer. I'm a race car.
Doc Hudson: Hohoho. Is that right? Then, why don't we just have a little race - me and you?
Lightning McQueen: Hohoho. Me and you? Is that a joke?
Doc Hudson: If you win, you go and I fix the road. If I win, you do the road my way.
Sheriff: Doc, what're you doing?
Lightning McQueen: Hahaha. I don't mean to be rude here Doc, but you probably go 0-60 in like, what? 3.5 years?
Doc Hudson: Then I reckon you ain't got nothing to worry about.
Lightning McQueen: You know what, old timer? That's a wonderful idea. Let's race.