The character played by Asia Argento is inspired by her half-sister Anna (Nicolodi's daughter from a previous marriage) who actually suffered from anorexia. Anna died in a scooter accident in 1994 shortly after the film's release, but she is seen in the actual movie during the closing credits dancing in the balcony.
Dario Argento's usual collaborating rock band Goblin were originally suggested to write and perform the music score for the film, but were declined by the American producers who wanted something more friendly to the American audience, therefore Pino Donaggio's orchestral score was used.
Piper Laurie revealed in 1997 that she never even bothered to see the finished film because she heard it was terrible, and that she and Frederic Forrest would constantly sit through the entire shooting laughing.
The trivia item below may give away important plot points.
Adriana Petrescu's death was much more violent in the shooting script. The wire was supposed to cut through her mouth therefore splitting her head in half and not through her neck. Tom Savini has also claimed Dario Argento wanted to shoot it from the inside of Laurie's mouth, so he asked to work on an oversized-mouth model in order to place the camera. But after Argento came up with the idea of the head saying "Nicholas", the set-piece was scratched out.