When Navin fills up the tank of the lowriders' car, he leaves the hose in the car and walks away. When he returns, the hose has been replaced back on the gas pump.
When Navin is being pursued by the sniper at the gas station, the sniper fills up the car's rear end with bullet holes. Later, after Navin escapes in the car without rear tires, there are no bullet holes visible on the car's rear end.
The telephone is visibly off the hook when Navin runs toward the garage to call in the stolen credit card.
When Navin first receives the glasses from Stan Fox, the part of the glasses that hook around the ears have almost no hook to them. After Navin installs the nose bridge handle (the opti-grab), the glasses have normal ear hooks.
When Navin is talking to the credit-card thieves, small ($1) bills are visible on the bottom of the pile closest to the driver and larger bills closest to Navin, but when the angle switches to Navin's. the bills closest to him are $10s and $20s.
When the new phone books arrive, Navin finds his name on a right-hand page in the phone book. However, when the madman randomly chooses a name to be his victim, he points to Navin's name on a left-hand page.
Navin opens his door and throws popcorn in the face of the Private Investigator, right after the popcorn bounces off the face the PI spits a mouthful out. The PI never opened his mouth prior to the throw.
When the madman is shooting at Navin at the service station, when the cans are shot at, the holes are formed from inside the can not from the shots fired at the cans. You can clearly see the aluminum fold outward from the holes in the cans.
During Catlin Adams's stunt where she falls off the bike after going through the flaming wall, the wire used to snag her off the bike is obviously visible during her ride towards the wall.
When Navin is chasing Billy on the train, his voice is not synchronized with the audio.
When the first oil can is punctured by the sniper, a tube can be clearly seen inserted through the bullet hole.
Navin could not have recognized the shooter turned private investigator because he had only seen him from a distance earlier.
When the family is sitting around the table for Navin's (Steve Martin) birthday, they congratulate him and his brother says "That's great, Steve!"