Creator Breakdown: Quite chillingly. Argento contemplated suicide for a few days after finishing the movie.
Dawson Casting: A somewhat bizarre example. Argento originally wanted the characters to be 12 years old, but the studio vetoed this idea because they were worried it would get the film banned. As a compromise, Argento hired actresses in their 20s, but retained the childlike dialogue from the script. He also made sure that all the doorknobs in the film would be above the actresses' heads, to make them seem smaller in comparison.
Also a young and dubbed-over Udo Kier is psychiatrist Frank Mendel.
What Could Have Been: Argento originally planned for the schoolgirls to be much younger than they were in the final product. His father, the producer, pointed out that the film would never be released anywhere if they went with that. He still had the sets constructed slightly too large, so as to maintain a sense of childlike desperation. The same script was used, which explains some of the childish behavior (like the "names of snakes" scene) the girls engage in.