No actors are given credit for playing Murphy's first three video victims: "Bart Bannister" (victim #1), "Terry Gotham" (victim #2) and "Phuc Nguyen" (victim #3). (Nor is there screen credit for George the Bartender.)
In the beginning of the movie, when Charlie is playing piano with his mom, Charlie is playing the bass line (sitting on the left). High, treble notes are then heard, but his mother's hands are not on the keys. Charlie was sitting too far to the left, and would have had to reach across her body to play those high notes, which he doesn't. Therefore, those notes couldn't have been played the way they were sitting and the way their hands were.
When Murphy is first introduced in the movie, in the scene where he is selling drugs in the bathroom, his cigarette is nearly done, but when he is giving Charlie a 'Swirly' his cigarette appears as it would right after being lit.
Principal Nathan Gardner: Everybody needs to vent a little now and again, don't you figure? Some of us are privileged enough to vent to you in the boys' room stall and the rest of us have to settle for less conventional methods, like, I don't know, a bottle of booze and a handgun.