I'd agree - though I think Irreversible is a great piece of work, I'm not sure its one on the 'human' level, if that makes any sense! Noé is a very internal filmmaker, to the extent that I'm not sure that he understands (or at least wants to understand) the wider world in which his self-obsessed characters operate more than as an evocative backdrop to the individual crisis situation, usually between a love triangle of characters. We never really see the aftermath of that excrutiatingly drawn out (another key Noé trait!) assault of Bellucci, just the character being stretchered out of the tunnel comatose to inspire our 'hero's' sense of blind vengeance in the opening scenes, but then her character as the film goes on moves from victim to liberated woman juggling the attentions of friend and boyfriend, to metonym for any future victim (in the scene kissing with the plastic sheet/body bag of the shower between them), to almost an 'Earth mother' figure in the
final 2001/Zardoz scene (strobing warning!), surrounded by children and nascently pregnant.
Even before it became impossible to ignore in extremely internal films like Enter The Void and Love, Noé seems much more interested in the individual reaction to events the overwhelms and transforms a character's worldview (Seul Contre Tous's incessant voice over and double-back ending factors in too). And he's also interested in the individual story being a grand metaphor for something, like the afterlife or in Irreversible's case the structure of the film going from all-male at one end to all-female at the other. The Gaspar Noé version of Straw Dogs would probably be something entirely from the Dustin Hoffman character's point of view (but I'd argue that Noé can be very interestingly complex when dealing with his frustratingly solipsistic protagonists - the leads of Seul Contre Tous and the recent Love are cut from incredibly similar cloth, just from different generations - even if that makes everyone else a cypher).
Whilst Peckinpah, for all his flaws, always seems like a 'social' filmmaker. He's interested in how groups of people interact together, and hurt each other. I'd argue that Peckinpah is as 'show-offy' in his own way as Noé, but the effects are added to enhance the audience's perspective on the mental state of the characters responding to their experiences rather than have the characters getting submitted to the metaphor into which they have been thrown as in Noé (I think the prime example of this for me is The Osterman Weekend, where the spy thriller material is incredibly weak, but it has a number of fantastic central scenes where Peckinpah can really get into the group dynamics of the bunch of friends being turned against one another. I think the Noé response to a similar lack of a core story would be embellishment of the environment around that central lack of narrative drive, as in Enter The Void).
Though I have to say that this isn't an either/or argument and its possible to find worth in both filmmaker's work. I find both Peckinpah and Noé fascinating! But they're pretty different and only linked here superficially through both Straw Dogs and Irreversible featuring powerful depictions of female victims of assault.
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On that note I still find that central scene difficult but in an interesting way. I go back and forth on whether that second rape was necessary to show or not, though think in the end that it was. I suppose the usual approach to the scene is that after the uncomfortable ambivalence in showing Amy's reaction to her old boyfriend forcing himself on her, this second assault suggests that she immediately 'punished' by the film all over again, and has to be to 'clarify' the situation as 'bad' for the watching audience (as if they had not been aware) and for Amy herself. That ambivalent reaction of Amy, emotionally estranged from her husband, enduring the brutal attention of the ex-boyfriend is extremely upsetting not just for the violation but also because it suggests that Amy might find this one potential avenue open to her, an escape from her stifling life that she would never have agreed to but now that barrier has been shattered from the outside there is a tiny amount of remembered affection there, albeit couched in hideous coercion (its what the commentators on one of the DVDs describe as the difference between an act of violence between 'people with history' and one without that). Its what makes Amy's reaction so upsettingly complex and potentially inflammatory, but also so powerful too, in the way that maybe she's only used to affection alternately bound up with cruelty and this is just the physical expression of it rather than the mental one with David.
Then that second rape shatters even that small consolation and reasserts the violation
as a horrific, unloving act of violence, in which Amy is used less for her body (as an object of lustful desires as in the first rape) but almost just as a object to forge a bond between members of the gang. He's a monster for having done this in the first place, but Charlie's reaction here is devastating too, having that (forced) reunion with his ex-girlfriend and then immediately being forced to submit himself to the needs of his mate. He's immediately fundamentally weak in that second moment (after trying to prove himself totally powerful and dominant in the first one) and has his own brief moment of, maybe delusional and in the moment hope (or at least remembrance and imperfect re-enaction of previous times) brutally shattered in a way similar to Amy.
It's such a complex scene of power dynamics (I love one of the commentators describing the action throughout, but particularly here, as "people thinking they are going to be able to act with greater restraint than they manage to"), and more than any other scene of this type that I've seen really gets into showing how the act of rape is as much an emotional violation as a physical one.
Then of course there are those fantastically brutal post-traumatic flashback edits throughout Amy's following scenes ("You can see...its not torn....at all") which show in no uncertain terms the lingering aftereffects of such an experience, and then how that in itself can affect the character's behaviour (and seep into Amy's reactions to other characters, particularly David and the town molester figure) after that. It often feels to me that the film never uses the character of Amy simply as a 'metaphor' (or as a conventional victim figure to be purely pitied by the film), and more as an individual character with her own reactions throughout, even if they might not be the 'societally right' ones to have had. Its a continuance of the approach taken to all of the conflicts throughout the film, both brutal but also compassionate in the sense that everyone's motivations in their interactions seem to be understood, if not condoned.