Since this is based on a book by "Twilight" author Stephenie Meyer, there's also (of course) a love triangle, with Jared (Max Irons) who loves the human Melanie and Ian (Jake Abel), who falls for the alien Wanda.
Moviefone sat down with the Irish star -- appropriately enough, on St. Patrick's Day -- where she was wearing green and also fighting off a cold. Over hot tea and with the hum of a humidifier in the background, she discussed the funniest day she had on set and all the ways people mispronounce her name
Moviefone: What's the hardest thing about playing two characters in one body? Ronan: One of the toughest things is there's a lot of tension and conflict between the two but they still need to have this relationship and this interaction. So you need to make sure that that comes across on the screen. There were some scenes where Melanie and Wanda have dialogue just between the two of them, which is straightforward enough. But when there's other people involved, or Wanda's ignoring Melanie or has to react to her for certain lines, you have to kind of map out where that comes in and how you want to go about it. That was the real hurdle that we came across.
How did you keep the characters straight in your head? For the majority of the film, I'm just Wanda, but every now and again, Melanie's will is so strong that she takes over. I think once or twice I may have done a Louisiana accent instead of the general American accent [that Wanda uses]. But it was pretty clear when it was Wanda and when it was Melanie.
You actually knew both Max and Jake before this. Yeah, I worked with Jake very briefly on "The Lovely Bones."
He told me you didn't recognize him when he came in to audition for this. No, I didn't recognize him, because he was quite a bit younger and he had longer hair in "Lovely Bones." He's a man now. And he's engaged! He's all grown-up. Max I had met a few years ago in this weird audition that we were both doing and had a bit of a laugh together. I knew everything was going to be fine with these guys. I know they're not pretentious or anything like that, which I can't stand. So yeah, it worked out really well.
Did you get any say in hiring them? Yeah, I did actually, and it was really nice to be involved in that. They could have cast someone who I didn't get on with at all. So it was nice that they called me in to do it. And it just felt right with both of them. It was kind of the obvious choice when they both came in. I didn't want two guys to be cast solely based on their looks. I was worried that that would happen and luckily it didn't. It was very important for me to know that they were going to cast someone because they were good actors, and they did.
You have a scene where you kiss first Jake and then Max. Tough day to film? It was a funny day. I was the butt of so many jokes. Just jumpin' from one guy to the next, it was mad. Those scenes where someone would get slapped at the end of the scene or someone got bitten or kicked, it was so funny.
So were you bruised at the end of that? [Mock dramatically] Emotionally.
The scene where Jared slaps Wanda, did he actually connect with you? Oh, no, no, no, no, no. He just goes like that [mimes a slap] and I react and fall on a rock. But we just found it funny that they hit me so much in that film.
Frances Fisher [who plays another human rebel] slaps you too. Frances actually hit me by accident and it bloody hurt as well. I had a few slaps.
Jake was also telling me that for his audition scene, you only kissed on the cheek instead of the full kiss you see in the movie. Yeah, it's fine when you're on set and you know someone, but that is so awkward when you're in an audition with someone to have to kiss them. Andrew was great because he said, "You don't do the audition kiss, just come really close and breathe" and that's what we did. It was just as intense.
You had to wear contacts for the film. How hard was that? Max told me he hated the ones in "Red Riding Hood" so much that he actually passed out. Oh my god. It wasn't that bad. My eyes are very sensitive anyway and I'm a bit of a flincher, so I was really worried that I wouldn't be able to wear these things because they'd be so uncomfortable. And they were for the first while, but then I got over it and it was fine. But a lot of eye drops, even when I wasn't shooting in the desert, you still needed so many drops per day because they just dry your eyes out.
Max told me he pronounces your name "Sir-sha" but IMDb says "Seer-sha." Which do you prefer? I say "Sir-sha," like "inertia," but a lot of Irish people say "Seer-sha," which is really the proper way to pronounce it. I'll probably never be a household name because of that bloody name. I'll have to change to, I dunno, Catherine or something.
How do people mispronounce it? Suarez. Sor-see. Sor-sha. Cerise, which is a completely different name. But Suarez was one of the best ones, I thought. Pretty exotic, actually.