I think the movie is a surreal cycle. it needs all of the characters to go on, over and over again. what if life is that after all? what is life after death one wonders? what if all the characters are living a same story from different points of view? there always needs to be a camilla, a betty, a diane, tho they play different roles. that's why "that's the girl" it had to be she for the cycle to go on
the key is certainty while the box is right the opposite, the mud lady is madness, it's the dark side of the guy who sees her, in fact they look quite alike. it's himself, his fears and all that.
i need to see the movie a couple of times more. maybe my opinion will change, who knows?

I not only meant Diane, Betty and Camilla, but Adam and Coco, the old couple and in fact, all of the characters. Who is the cowboy? He's a messenger. Who is the guy on the wheelchair; the one who sets the wules. Like in all orders of life, there are people who set the rules, those who impose the power.
I don't think the masturbation scene is at all relevant. Yes the coffee cup and ashtray because they appeat in two different places, that is the diner and Diane's place. Why? Because not only characters change roles, but material things as well. Are the hit man and the soon to be dead guy talking about the same accident? I don't think so. What about the accident site? It is on top, and from there all starts going down, till the very bottom of things. Like going deeper into the story. That scene shows the surface only.
More to come...