 Director Dario Argento (qv)s original idea was that the ballet  school would accommodate young girls not older 12. However the  studio and producer (his father) denied his request because a film  this violent involving children would be surely banned. Dario  Argento raised the age limit of the girls to 20 but he didnt  rewrite the script, hence the naivety of the characters and the  occasionally childlike dialogue. He also put all the doorknobs at  about the same height as the actress heads, so that they will have  to raise their arms in order to open the doors, just like children.