The film explicitly states at the beginning that Amira Casar's sex scenes were done with a body double. Indeed, Casar allegedly told her male co-star Rocco Siffredi that she would not be having sex with him for the purposes of the film. Interestingly, Siffredi himself had a porn double for the opening gay fellatio scene.
For the close-ups of the female sexual parts, Catherine Breillat deliberately chose a body double for Amira Casar who was quite hairy. This was to counter expectations of female nudity in film and also to reinforce the male character's aversion to what he sees in a naked woman.
In reference to the scene where 3 little boys play doctor with a girl their age, some sources have claimed that those few frames of the girl's vagina are of a prosthetic dummy, but as the girl can clearly be seen breathing, this cannot be the case.
Unlike Romance (1999), where Ducey filmed even the most explicit scenes, Breillat allowed her female star Amira Casar to use a body double in Anatomy of Hell (2004). Siffredi's performance, however, is all his own work.
His frankness, a by-product of 20 years at the hardcore end of the business, is one reason for Siffredi's new-found status as a film festival darling. He is very defensive of Breillat, who wrote the male part with him in mind and has no qualms about showing his co-stars exactly what she wants.
"I think Catherine has a lot of sexual fantasies and unconsciously she may want to sleep with me," he says. "When she was explaining one scene to me she took my sex in her hand and explained to Amira how she should play the scene. Once she said to me that, if she was younger, she might have played Amira's part herself."