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.
Deliberate mistake: The monitor from inside Mack's trailer displays his whole face while talking to McQueen. There is no camera outside of Mack that can display him in that fashion.