Re those 'tag-team' sex scenes ....
I just saw the DVD for the 1st time. Interesting movie, beautifully cast and produced, lovely music, but in the end, a bit hollow. The psychology of the characters was, imo, not particularly well developed.
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One question in particular:
Why did they think they had to have both Carlo (Farinelli) and Riccardo (his brother) in on the sex scenes? Unless there is some historical evidence the two Broschis actually practiced this sort of sex, I don't see the point, except (presumably) to excite the audience's prurient interest. From all I've read (not all that much, admittedly) castrati did OK in the sex department quite well without needing the help of "real" men to complete the act. They were, in fact, very popular with the ladies -- in the cliche, the rock stars of the day, and, like rock stars, they had plenty of groupies.
The fact that a woman could have an affair with a castrato without any fear of getting pregnant I would assume attracted rather than detracted, in an age when there was no reliable birth control, so why would you want to risk a pregnancy by bringing in a second lover?
I do understand why both Broschis would be involved in the final sequence with Alexandra -- clearly both Alexandra and Carlo wanted a child, and Riccardo was the means to get one -- but in the earlier sex scenes, Riccardo struck me as an unnneeded third wheel.
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(I'm assuming that much of the Carlo-Riccardo relationship as presented in this film was fictional any way.)