Near the end, when George Stark is holding Thad's twins his gun is a Colt 1911 (as he's had throughout the movie). When Thad moves closer, the gun changes to a Beretta 92FS. After Thad takes one of the twins, George's gun is again a 1911 when he tucks it in his waistband.
In the scene where Thad is writing in his office with the sparrows on the window, the sharpness of the pencil he uses changes back and forth from very sharp to very dull. This is the scene where Thad stabs himself in the hand.
George Stark, Thad Beaumont's alter ego, was supposed to be from Oxford, Mississippi, which is in Lafayette County. The Mississippi license plate on his car incorrectly said Harrison County, which is on the coast of Mississippi at the opposite end of the state from Oxford.