Since Daniel already knew Farhad isn't fluent in English, instead of constantly saying he "replaced the lock", why didn't he just say "he fixed the lock", he would've Farhad satisfied as a customer and therefore resolving the misunderstanding and Daniel would be paid for his services.
When Officers Ryan and Hanson pull Cameron and Christine over, Officer Hanson turns his light on while still in the car. When they are out of the car, his light is off, but in a later shot the light is on again.
When Daniel is leaving his daughter's room after the cloak story scene, he pauses at the door to look at her. The light switch is in the down position and the lights are on. We see the daughter in bed with the lights on, and then cut to Daniel about to leave the room where the light switch is still down, and he pretends to flip it down as the lights go off.
When releasing the illegal Asian immigrants from the stolen delivery van, the internal cage door is open. In the next shot, it is already closed when the outer van doors are shut, even though nobody closes the cage.
When the Persian is holding the locksmith at gun point, the daughter runs out the door, the door swings and stays open. The next shot, the mom runs to the closed door. Next shot the door is back open again.
When Graham is investigating the Conklin shooting, the blood stain pattern and bullet hole position on the Mercedes window is different between the pan out view of the dead driver and when Graham approaches the vehicle and picks up the gun.
In the part where Officers Ryan and Hanson pull Cameron and Christine over, towards the end of the scene when Officer Ryan walks back to the driver side, a shot is seen of him entering the vehicle. When a later, wider shot takes place, Officer Ryan is seen leaning inside the vehicle from outside, and then opening the door and entering the police car.
In the beginning when Graham is examining the shoe with his pen, he touches the top near the laces. Later, when the movie comes back to this scene and he is examining the shoe, his pen touches a different part.
When Daniel comes in to speak with Farhad after fixing his lock, two members of the production crew can be seen attempting to hide behind one of the store shelves in the bottom-left corner of the frame.
When the gun store clerk is listing the "types" of bullets that will work in the gun, he says ".45 long Colt". This is a caliber not a type and too large a caliber to fit this revolver. A later closeup of the box of ammunition confirms the gun is a 38 special.
When Cameron pulls over to the street corner to let Anthony out of the car (after their run-in with the police), you can see Anthony's legs getting out of the car. Then they are back in the car talking and only then does Anthony get out.
Shaniqua tell Officer Ryan his father's urinary tract infection is not an emergency, even though she tells him she's not a doctor, she's informing him the policies and standards of his insurance carrier doesn't consider this an emergency.
Partway through Officer Ryan's rescue of Christine from her overturned SUV, the camera ran out of film, as evidenced by film sprocket holes appearing in the frame. This is an acknowledged goof from director Paul Haggis.
The police cars have subtle difference from real LAPD patrol cars. The real cars will have "To Protect and to Serve" on the door, to the right of the City Seal. The cars used this film have "To Serve and Protect" and its writing is to the left of the city seal.
The goof items below may give away important plot points.
After the Persian store man discharges his weapon on the girl, the next scenes clearly show that the revolver's hammer is still cocked and ready to fire. The shocked store man would have had to manually re-cock the weapon again for this to happen.