Julie Carmen had never done any prosthetic makeup prior to this film, and she was so freaked out when they made the life mask of her head that she had a panic attack as the plaster hardened and then went home and burst into tears about the experience. As soon as she regained her composure, Carmen received a call from a crew member informing her that there had been a problem with the mold and she'd have to do it again the next day.
As it was scripted, the fight sequence in the library was intended to be a more elaborate battle which resulted in all of the bookshelves toppling like dominoes.
The movie never explain what happen to Amy, Charlie mention her once at the beginning of the film to his therapist. It either they broke-up or she want to different college.