When Ludlow and Wander fight in the end the handcuff that is placed on the railing changes positions after the initial "lock up." The handcuff moves one section down the railing and is closed tighter.
After getting into the fight with the two Korean men, Ludlow has blood on his forehead. During the scenes where he bust into their house, in some shots he is seen with the blood on his forehead but in other scenes there is nothing on his forehead.
When Ludlow shoots the Korean guy who was sitting on a toilet, he falls has his pants on and the toilet seat is actually down. Later, when Ludlow plants the weapon on the guard at the desk, the toilet seat is up.
The position of the sun changes in the last scene.
When Captain Biggs sits across from Ludlow at Ludlow's desk and starts talking with him, his necktie alternates from being outside of his lapel to under it, although he does not move.
One of the thugs in the convenience store shooting uses a sub-machine gun chambered 9mm, Ludlow's revolver is chambered in .38 special. These two bullets are the exact same diameter and it was covered up that Ludlow was ever even there in the first place. There would have been no reason for a medical examiner to think or try to determine that one bullet came from a different gun.
When Ludlow is tied up and being shot at by the other cops outside the house in the hills, the red plastic cases of the squibs are clearly visible as they explode around him.
In one scene when Ludlow is exiting his vehicle he remotely locks his car as he walks away but while exiting it was clear that the driver's window was down.
Must be CGI, but the sun rises, in the beginning, and sets, near the conclusion, behind the same hills.
When Tom fights the captain in his home and they are both on the ground, we can see a moving shadow on the wall in the background.
When Ludlow and Diskant are at Grills' house, just after they beat him with the telephone book, someone disappears through a door in the background and in the next shot the door moves and closes. If someone else was supposed to be in the house, someone would have noticed and/or mentioned it...
When Keanu Reeve's character rescues the twins at the end of the shootout with the Koreans, it's shown that the door to their cage has soundproofing material on it, but later when he details the events that occurred to the police committee, he mentions he only entered the property because he heard screams, which would've been impossible with the soundproofing material used on their cell, and the committee does not point out this contradiction.
Ludlow says that his wife died because she had a blood clot in her brain, and it burst. Blood clots do not "burst." What is meant is an aneurysm, a structural defect in a blood vessel.