Other mistake: When Somerset goes back to the man's house alone, he cuts a sticker on the door with his switch-blade to get in. The first error is the sticker is on the inside and it says "Keep Out." The best part about it is the door opens inward. How did they put the sticker on the inside and then exit? (00:20:45)
Other mistake: In the scene where Mills hears the phone ring while they are investigating the killer's house Mills runs down the hall way and slides on his knees to get the phone. You can clearly see the knee pads on his right knee.