[This story contains major spoilers from season three, episode eight of Yellowjackets, A Normal, Boring Life.]

When it was announced that Hilary Swank would be joining Yellowjackets, who she was playing was kept secret. As the third season began to roll out, the Showtime series heavily hinted that a character from the wilderness past was perhaps haunting Melanie Lynskeys Shauna in present day. For anyone who guessed that Swank would make her debut as the adult version of that person, you were right.

In episode eight, A Normal, Boring Life, Swank arrived as Melissa, a new older (as the cast of the hit Showtime series calls them) for the teen played by Jenna Burgess in the 1996-97 timeline. Swank plays one of four new characters introduced this season, following the wilderness debuts of Joel McHale, Nelson Franklin and Ashley Sutton. Teen Melissas role expanded in season three when she explored a new relationship with Shauna (played by Sophie Nlisse in the teen version). Its a veryYellowjacketsromance, co-creator Ashley Lyle had said about Melissa and Shauna. I wouldnt say romantic is the greatest descriptor, but theres a lot of energy and its a relationship. We liked the idea of Shauna becoming the sun to someone elses moon, especially with how shes emerging from all her grief and anger and rage [afterlosing Jackie and her baby]. Nlisse, meanwhile, had hinted that the teen romance was not going to end well: I think Shaunas incapable of loving and receiving love at this point in her life and so sadly, I dont think it evolves into anything great.

When Swank returns to the story in present day as grown-up Melissa, Shauna confronts her ex after finding out that Melissa took on a new identity and married the daughter of Hanna, the frog scientist played by Sutton who the group will eventually do something terrible to (shes still alive in the wilderness timeline). Melissa fires back that she faked her death so she could start over. Shauna tells Melissa that she doesnt deserve a normal life and attacks her, pins her to the ground and takes a bite out of Melissas arm. The episode ends with Shauna dangling the bloody piece of flesh over Melissa, demanding that she eat it, or shell tell her family who she really is.

Below, the two-time Oscar winner talks to THR about joining the cast for the end of season three and fighting Lynskey, while also revealing what her arm flesh was made of and why Melissa decided to poke the bear.

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The secret is out, you are Adult Melissa. How did this role come to you?

I got a call from the creators asking if I wanted to be a part of the show and I said, Tell me more. What they shared with me was super intriguing and I said, This sounds like a blast. Im totally game. I didnt get to read anything first because they didnt have anything yet. They offered this to me two weeks before we started filming.

Oh, really?

Yeah. So it was just as much of a surprise for me as everybody else. It ended up being exactly that, a blast. The actresses on the show, theyve been doing it and are still loving it. With Melanie, I love the unexpected choices that she makes as an actor. Thats the beauty of Melanie, she makes unexpected choices in her deliveries that are beautiful, and I dont think a lot of actors can do that. So hitting it back and forth with her in that serve-and-return was really a lot of fun.

Did you have time to talk to Jenna Burgess about forming the character of Melissa this season? Youre each really introducing her in different timelines.

Yes, she did more before I did, so I was very keen on having a conversation with her and hearing what her relationships were with the younger people that I am now going to be playing with as their older versions. She actually did a lot of my homework for me by informing me of all that.

So they pitch you this arc. What was your first day on set like?

Episode eight was filmed in order, which is really rare. We filmed at Melissas house and getting to do it in order was really helpful because it was a lot of dialogue and I was just stepping back into doing something postpartum. Your brain just doesnt work as well, I hadnt used that muscle in so long. So filming in order definitely helped me ease back in. And it was so great to have all that dialogue because youre like, Who is guilty here?

Hilary Swank as Adult Melissa in episode eight, A Normal, Boring Life. Kailey Schwerman/Paramount+ with SHOWTIME. Had you and Melanie Lynskey ever met before?

No, we had never met. We said hi to each other and that we were fans of each other, and then we got into it. When you get to work with someone that you admire, its always a fun thing.

The dialogue between you two brings a lot of history to that kitchen table. Melissa basically says: Im living this normal life; I go to church and I have a kid and a wife, look what Ive done for myself. Shauna counters: But youre a liar and your life cant be normal. Do you understand where Melissa was coming from in her decision to fake her death after rescue and start over?

Oh yeah, I really feel like Melissa had moved on in the best way she could. I think she was really trying to piece together a normal life. Little does she know that its not so normal to marry the daughter of somebody that you have done something terrible to! [Note: In present day, a tape related to Hannas death has been haunting the adult survivors.] But I think thats her way of loving that person in a way that she felt like the person who got hurt [Hanna] would have liked. Its her way of coming to terms with it. Although, she says she didnt mean to fall in love with her, that it just happened. But I think subconsciously, so much more is at play that were not aware of.

We see in the wilderness how badly things are ending between Melissa and Shauna. We have yet to find out what happens after they are rescued, but Melissa says that she felt like she wasnt one of them once they got back. What do you imagine happened?

I pieced together that she really tried to move on. She has a choice. She can either sit and stew and have nightmares about what went on, or she can try and heal and make some type of peace with it. I really believe that. But I think what happens when youve gone through something traumatic and you start getting triggers, the trauma thats still in your tissue starts coming out and you dont have control over it.

Melissa says Shauna creates drama and theres an explanation for all of the things that have been happening to her. Of course, we know Shauna is not going to take this all lying down. Why did Melissa poke the bear?

I dont think she thinks Shauna is going to kill her, and if shes going to try and kill her, shes going to give it a good fight back. I dont think shes goading her on purpose, I think that Shauna is trying to take these jabs at her and then Melissa is like, Really. You want to talk about it? Its pathetic what youre doing. I think Melissa is just saying, Come on, grow up. Were past that. Were moving on. And then Shauna is saying, Oh, no, were not. Youre not moving on because I havent moved on. There is still trauma for all of us and let me remind you.

When you read in the script that they were going to have this knock-down, drag-out fight, how did you react to that twisted cannibalism cliffhanger?

I didnt even know that was going to happen, because I signed on without reading a script. When I read it, I just thought, these are people who are stunted. Their emotional world was stunted because theyre acting like 2 year olds: Im going to bite you because youre not listening. Thatll make you listen!

Melanie Lynskey as Adult Shauna after taking a bite out of Hilary Swank as Adult Melissa in episode eight, and demanding she eat it or she will tell her family who she really is. Kailey Schwerman/Paramount+ with SHOWTIME. When filming that fight scene, did you do your own stunts?

Yeah, we did all of them. We had someone there, because you have to, insurance-wise. I think a lot of time, they also have a stunt person there just so you dont get tired and so you can do all the dialogue. But yes, we were doing them. We knocked it out in one day. You gotta clean up [the blood] and do different angles, and do it all over again.

What was a highlight of filming that fight sequence?

I think the highlight of being physical is that when you have all this heady dialogue, its nice to have a change of pace. Usually actions action and dramas drama. When you get both of them in the same space, its really nice because sometimes when youre just doing action, youre like, I would do anything for dialogue right now. And then when you have so much dialogue youre like, I need to move. So its a beautiful balance.

The fight ends with Shauna taking a bite out of Melissas arm, pinning her down and demanding Melissa eat her own flesh. What was her arm made out of?

I think it was silicone. Like chewing on silicone. [Pauses and reacts to my reaction] Is that a bummer for you, did you want me to say it tasted like flesh?

Well, when they talked about eating Jackie (played by Ella Purnell) in season two, her corpse was made out of jackfruit, which they then called Jackie fruit, and a lot of them ended up gagging.

Yes, to be vegan, so instead of having chicken or something they had jackfruit. Yeah, mine was just silicone. But Im happy because I eat a lot of jackfruit and I wouldnt have wanted to tarnish my jackfruit!

This episode ends with Shauna saying, Eat it, and you saying, What the fuck? The fight escalated so quickly. What is Melissa thinking at the end here?

I think shes like, I thought I put all this behind me. I cannot believe youre doing this. You really are seriously messed up that all this time later, youre coming here and biting my arm off. I think shes honestly like, what is going on?

Your arrival, to me, tips the scale in this larger conversation about Yellowjackets and whats mystical and what is explainable. Coming into the show at this point, what was your take on the unanswered questions?

Even after doing those episodes, there are still a lot of unanswered questions. I think its ever-evolving. Thats the beauty of being able to bring in a new storyline. There were so many young women there in the beginning who crashed, you can really have a field day with that. And thats so rare to be able to have that many different opportunities for stories. But I dont think anythings answered. I think people are going to get to the finale and be like, What?! Because I was like, What?! And Im in the show.

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Yellowjacketsseason three releases new episodes Fridays on Paramount+, with a linear airing Sundays at 8 p.m.on Showtime.Follow along withTHRs season coverage and interviews.