The thing about Marilyn Monroe is she's not like anyone else. She's not like you, and she's not like me. She's not a regular person.
She couldn't get away with playing one, either. Whether or not that inability to take on "straight roles"--i.e., regular people--contributed to her personal tragedy, it also enhanced her ability to play parts sympathetically that another actress might have made shallow or unlikable--Lorelei, Sugar Kane, my personal favorite Pola Debevoise, and others in her light comedies. A lot has been said about her time with Strasberg, and how that intense training might have hurt her career rather than helped it. I can see where those arguments are coming from. The key to Method Acting is pulling out the raw, human element at the center of the performance. And that is the opposite of Marilyn's talent: the talent of creating a real, relatable character out of mannerisms and motivations entirely devoid and innocent of ordinary Earthling trappings.
This quality really has little to do with her actual looks. She's extraordinarily pretty, yes, with a body I'd personally kill for. But there are plenty of extraordinarily pretty, curvaceous blonde actresses out there: Anita Ekberg, Diana Dors, Mamie Van Doren, Kim Basinger, and these days, someone like Scarlett Johansson. And you know what? I might even argue that on a sheer physical level, some of those actresses are even prettier than Marilyn. What separates Marilyn as an icon is what everyone else has already talked to death: her spaced out, otherworldly vulnerability--the ultimate childwoman.
What makes her Nell Forbes in Roy Ward Baker's Don't Bother to Knock so incredible is how she subverts that innocent yet sexy childwoman image, that at first so tantalizes Richard Widmark's Jed Towers, into something terrifying.
I once said about Vivien Leigh that she didn't so much act roles as she did throw herself at them. Marilyn is acting here, but she's bringing something out of herself that while present in other roles, has an edge here that spooks you. Nell is popularly known as her "psychotic babysitter" role, but she makes her much deeper than that. Of course, Daniel Taradash's screenplay has much to do with that, as well; according to what I've read about Charlotte Armstrong's original novel, the Nell in that story (with the surname Munro that they had to change once Marilyn was cast) is far less sympathetic, without the tragic-lost-love past they give Nell here.
They probably added this backstory once they saw what Marilyn was doing with the role. This was her eighteenth movie, and Fox had figured that since she had already proven herself unusually sexy in movies like All About Eve and The Ashphalt Jungle, they might as well make a cursory attempt to prove she could act a little. She must have unnerved even them with the final product.
You don't see the wheels turning in her Nell. She appears like a luminous vision across the courtyard to the jilted Widmark, recently dumped by Ann Bancroft (luminous in her own right, in this her film debut). Nell, recently released from a mental institution into the care of her jittery elevator attendant uncle Elisha Cook, has secured a brief babysitting position, thanks to her uncle's insinuating ways around the luxuriant hotel where he works. When Jed sees her in the window, highlighted by dim lamps, she's attired herself in the wife's negligee, a midnight-colored affair, and she's also wearing star-like earrings and bracelets. She's sashaying back and forth in front of a mirror, waving the negligee around like a mermaid gracefully flapping her tail. She seems the ultimate night-time dream of a woman perfect for forgetting your woes in.
What Jed quickly finds out is that Nell is really a nightmare version of a man's ideal one-night stand. Her stardust and hare-brained, loopy manner, Marilyn's chief charms in her future projects, is the chief signal something's wrong here. We can tell from the start. The instant we see her wander into the hotel's lobby, we immediately interpret her dazed otherworldliness as broken-hearted derangement, not the airs of a kooky, lovable ditz, the type she popularized in her comedies. Her interactions with her uncle in the elevator (and does anyone else get the feeling Cook's character ain't quite right, either? Dude, seriously, back off the guests!) increase the feeling she's just barely able to keep her feet on this planet, her head in this hemisphere. By the time she's left alone with the little girl, we know that somehow, some way, the little girl will be horribly effected by the off-balance big child in charge of her. And yet we also know that on some level, anything Nell does to the child won't be out of malice, but out of frustration that the child is not playing along in her own skewered, emotionally stunted take on reality.
And that strange innocence is far more terrifying than if she were a frank sociopath. She may be the closest equivalent to a female Norman Bates I've yet seen in a movie.
Jed, presented as one of those hard-boiled, jaded heavies always hanging out in Noirs, can't handle her because of this. If she were your standard femme fatale, along the lines of your Jane Greers, Linda Darnells, Gene Tierneys, and Lauren Bacalls, he could set her straight right away. But all his hardest, most biting lines fail him, because Nell is actually hurt by them. She's technically a femme fatale--her sex appeal lures the hero into dangerous, violent entanglements--but she isn't at the same time, because she's delusional, tender, and frightened. She just wants her lover back. Yet she ties up a little girl and tries to push her out the window. He can't reconcile this. Unlike your Sam Spades and Phillip Marlowes who had to rely on their brutal wits to win the day, Jed has no alternative but to empathize before the conclusion--really empathize.
That Nell succeeds, through her insanity, in creating a good man out of Jed is what keeps her from becoming a villain in the true sense of the word. The movie is a strange blend of Noir cliches--all the business with the shades, Bancroft's tedious songs in the inexplicably Western themed nightclub, the tacked on sentimentality--but combines them with innovative, risky touches, like revealing the self-inflicted scars on Nell's wrists and upping the tension by filming in real time.
But really, again, the most innovative part of the whole movie is the alien-like Marilyn. She doesn't play fragile, she is fragile. That may sound dunder-headedly simple, since of course Marilyn is known for her sincerity. But the impact of seeing such broken, teetering fragility, actually seeing it, without feeling like it's just being played out for you, is shaking to witness. There are cringe-worthy moments, where you can't bear to hear her baby voice moon ecstatically over her lost airforce pilot (just how healthy and mature was her love for him? Surely her childish instability wasn't created overnight by his death but by systematic abuse and natural impulses). But these moments are cringe-worthy for all the right reasons--you don't think you'd be able to listen to someone saying that in real life, either. It's too pathetic and heartbreaking.
I've yet to see Niagara, but I've often heard it criticized for spinning Marilyn's unique charm too negatively in that villainous role, which this movie skillfully avoids by allowing Marilyn to interpret Nell on her own terms, with her own vulnerability. Does such wistful madness make her performance more difficult to watch, knowing the ultimate end the movie's star came to? Yes, in a way. But on the other hand, you're almost affirmed on Marilyn's behalf, watching her in such a triumphant performance, knowing that without any outside prodding, Marilyn was capable of using her own natural self not only to charm, but to genuinely move and disturb.