One of Them Is Not One of Us in M. Night Shyamalan's 'Split'
The movie's version of Dissociative Identity Disorder is not science, but metaphor, and horror movie metaphor at that.
"Why do you act like you're not one of us?" Angry and scared, Claire (Haley Lu Richardson) lashes out at Casey (Anya Taylor-Joy), while a third high school classmate, Marcia (Jessica Sula), looks on, terrified. Their upset -- individual and collective -- is understandable, as the girls are locked in a basement, kidnapped.
That said, as M. Night Shyamalan's Split begins, you're all too aware that Claire's accusation is not only a response to their immediate trauma. Just before, during Claire's birthday party at a King of Prussia mall restaurant, she and Marcia rolled their eyes at Casey as she stood alone across the room, calling her a "mercy invite", which is to say, not one of them, the cool girls. Following an especially well-edited scene in the parking lot, during which the girls' slow realizations that the man in the driver's seat is not Claire's dad but rather Kevin (James McAvoy) come together in a series of vivid close-ups, all wide eyes and tight spaces.
Here in their basement cell, Casey is again set across the room from Marcia and Claire, who sit together and hold hands in solidarity. When Kevin appears in their doorway, looming in a low angle shot and then deciding to drag Marcia off with him, Casey gives her a plan: "Pee yourself," she hisses. The gambit works, and within seconds, their assailant pushes Marcia back inside, visibly repulsed. The girls confer: Casey urges caution, or "He'll hurt us." Claire calls that "victim shit", and then they learn something else, something you already know because you know their film's title: the kidnapper suffers from Dissociative Identity Disorder.
Most horror movies operate along these lines: you know or can guess more than victims might, those victims are girls, typically teenagers in tight sweaters or short skirts, as they are here, with one standing out from the others, as Casey does here. You're also familiar with the concept of the predictably unpredictable monster. Just so, Kevin appears in various scenes, variously transformed, his clothing or affect indicating which of his 23 alters he might be. The film manages this array economically, showing only a showy few (the nine-year-old, the woman, the artist), while indicating others in conversations between Kevin, as Dennis pretending to be Barry, with his therapist, Dr. Fletcher (Betty Buckley).
This too is a convention in this horror movie subgenre, the doctor who means well but doesn't grasp the complete horror of her patient. As that horror expands, Split offers a metaphorical sort of splitting, intercutting scenes at Fletcher's home (also her office), the girls huddled in their cell, and Casey's flashbacks to her five-year-old self (Izzie Leigh Coffey), in the woods deer hunting with her father (Sebastian Arcelus) and uncle (Brad William Henke). Of these pieces, Fletcher's struggles, alone and with her patient, provide the usual galling trajectory as you're increasingly aware of how wrong she is, long before she's aware.
The movie indicts Fletcher's wrongness even within her own world, as she advocates for her DID patients, making a case that her peers reject outright. Not only do the patients have access to special emotional or psychological levels, she theorizes, but they also embody physiological differences (one of Kevin's alters has diabetes, for instance). Granted, it's not science, but metaphor, and horror movie metaphor at that. But even in that context, the logic is thin, and therefore distracting.
As much as you worry for Fletcher, so obviously bound to pay for her misreading, you know your primary object is Casey, as her story intersects ever more insidiously with her captor's. Her childhood episodes don't quite run parallel with his, but each set reinforces how memories and traumas create cycles. Casey's efforts to manipulate the nine-year-old alter ego, Hedwig, begin with sharing secrets: "I get into trouble at school on purpose," she tells him, so that she's sent to detention, "So I can be away from everyone, so I can be alone."
She's never quite alone, of course, as she's also, always, judged and punished by people around her. Just so, Hedwig can hardly be alone, being one of 23 living in one body. Still, Split suggests, they perceive themselves to be alone, as well as survivors of brutal judgments and punishments. In drawing plot comparisons and emotional connections between monster and victim, the movie invites a rethinking of horror's reductive moral poles, for a moment, anyway.
Here, in its simplest terms, monstrosity is the result of surviving trauma and then inflicting it on others as vengeance. As the Last Girl, too, is a survivor (and a horror movie convention), the movie stops short of revealing how she'll process her many traumas. But it does leave her alone, and seeing herself alone, seeing herself as "not one of us". Let's hope there's no sequel.