Male Genitalia and Casting
To be honest, the really transgressive part of the sex in this movie is the erect penis, which is usually reserved for porn. Noe must have known he was going to be shooting a movie that was going to be showing a lot of dick. So, how much do you think that factored into casting? Did he explicitly want a circumcised dick, was he looking for average size (like did someone come in and their dick was too big or too small), was he making sure there were no weird bends or other strange things going on.
Also was the silhouetted blowjob the main actor's dick? Felt like it was smaller than when seen in the rest of the film.