Revealing: When Jake "kills" Chelsea, and his phone starts to ring, the phone is blinking, and vibrating. It falls to the floor, and Jake reaches for it, when he does this you can see that the phone is not actually ringing, because the screen is dark and the screensaver is active.

Continuity: At the beginning of the movie, the car the characters take to the party has European plates. Later on, the plates are American.