Say what you want about M Night Shyamalan (and a lot of people have since the release of The Happening and The Last Airbender), but the release of Split went a long way to restoring faith in him as a film-maker. It also set up the exciting prospect of a third movie in his Eastrail 177 Trilogy that will reunite Mr Glass with hero David Dunn while also tying them to Split's The Beast.
Crucially, it was a return to form for Shyamalan, who knows a thing or two about story-telling that dupes the audience into believing one thing and then sucker punches them with a "he was dead all along" sort of twist. And Split obviously had that in the shape of Bruce Willis' cameo as David Dunn.
But what if there was an even bigger twist that nobody seems to be talking about?
That's the way Reddit user Tehsideburns sees it as they've stumbled across what they claim is a very obvious twist. It's pretty smart on first look: the theory suggests that Casey is in fact another of Kevin's multiple personalities, which was initially inspired by him not spraying her like he does the other two to incapacitate her when he abducts the three girls:
"...I thought it was so obvious that the girl in the front seat was just another one of his personalities, and that the end of this film was totally going to have a fight club / primal fear moment. Everything I saw throughout the entire film supported this theory - that Casey IS Kevin - and I couldn’t find anything to directly contradict it. Imagine my joy when the movie ended, the credits ended, and this revelation never overtly happened on-screen, at least not in an obvious way."
The original post points out further "evidence" behind the theory. First, that Casey's name is a give away - Casey = KC = Kevin Crumb; second that she and Kevin share profound trauma; the fact that he doesn't spray her in the car, that she's separated from the other girls visually, the way Kevin talks to the girls as if she's not there occasionally. There are other points in there, like Kevin and Casey's shared passion for art, and it all reads pretty well.
There are certainly some issues with it, and the comments section have offered rebuttals, but it does almost feel like Shyamalan intended us to believe that Casey was a personality of Kevin's - even only subconsciously with those triggers of familiarity. That he wanted us to expect another twist and perhaps that the twist was that there was no second twist - no revelation that some would see as obvious.
If that is the case, he's definitely operating on a level close to his story-telling best. In either case, in fact.
So what do you think? Did Shyamalan want us to believe that Casey was Kevin's 25th personality? Was she genuinely a construct of his psyche? Or is this theorist reading too much into things?