Given the film's boffo box office, chances are that you have already seen "Glass," M. Night Shyamalan's conclusion to the superhero saga that started with "Unbreakable" and continued with "Split" (so, of course, Bruce Willis, James McAvoy and Samuel L. Jackson are back). And, given that this is a Shyamalan film, it ends with a pretty colossal twist.

We spoke with Sarah Paulson, who costars as the psychiatrist tasked with unraveling the truth behind the supposed heroes, about what she knew about thw twist and what her favorite element of it was. Beware, because, of course, SPOILERS.

Moviefone: How much did Night tell you about your group, The Clover Folk?

Paulson: [laughs] The Clover Folk! The secret society? You know, he told me but it was all there on the page. That's all that was there. The biggest question was which hand was the tattoo going to go on. And I have not seen the movie so I wonder if this is a thing people will notice on repeated viewings, but we did versions where you see the tattoo before we see the tattoo with Bruce at the end of the movie. I don't know if, when I'm looking at Sam's X-rays, we did versions where you could see a little bit of it. I don't know where Night ended up with that in the edit.

But that was the main discussion – where do we put it, where are we going to see it? Let's do versions when we see it here and he'll decide if we ever see it when he's editing it.

That's so interesting. Now I want to go back and look for it.

I know. I wonder… Because if you're not really looking for it, you wouldn't notice.

You weren't pulling down your shirt sleeves or anything?

No, it was very much an issue during costume fittings, to make sure all of my sleeves were, on its own, able to conceal it without much effort and if we wanted to reveal it, we could.

Did he ever indicate that this was an idea that he'd had from the beginning, with this group that shadows these heroes?

Well, listen, the man had almost 20 years to think about it. So whatever he decided, he decided long ago, but because he has so much invested in this, because the characters are so beloved to him, he would sometimes be like, "No, I do want to see the tattoo beforehand!" or "No, I don't want to see the tattoo!" He wanted to be able to have the option in the edit.

What was your favorite aspect of this element?

I like playing everything about her. It's always fun to place a person with a secret. At the same time, if you have a secret, you've got to be really good about concealing it. I haven't seen the movie but I've talked to people who have and they've said, "You think there's something mysterious about her but you don't think like this happening." You're never sure if she's good or bad.

"Glass" is now playing everywhere.