Brilliantly manic but decidedly unimposing, Charlie Day doesn’t seem like the most obvious actor to be cast in a sweeping sci-fi opus like 'Pacific Rim.' But in Guillermo del Toro’s new film, Day is perfectly cast as a fanboy scientist who is as fascinated by the gigantic monsters that are attacking humankind as he is determined to stop them. He not only serves as some much-needed comic relief in the film, but provides a human counterpoint to the monolithic heroics of his co-stars, while occasionally providing a few details that become crucial to the plot.

We sat down with Day to talk 'Pacific Rim,' where the actor discussed the challenges of squaring off against one of those megaton monsters – and revealed it was pretty easy, even when they weren’t actually there. Additionally, he talked about tackling different sorts of acting challenges, in particular his openness to take on roles that push him outside the realm of comedy that he’s already conquered.

It feels like you’re giving a performance that is a little bit like an anime character – the scientist who’s incredulous at what’s going on. When you took on the role, what were you thinking about in terms of what or who he is?

Well, I knew I had a little bit of an interesting challenge which was the bring some levity to the movie, and some humor, which was why I was getting the job. But also hopefully be real and deliver information in an interesting way, and then I had the challenge of there were certain sequences where you’re worried about whether I’m going to get eaten so hopefully to pull all of that stuff off. But if anything I was just excited to get to do something slightly different than what people know of me or expect.

Is what you just described the same thing that Guillermo asked you to do?

Guillermo and I would always talk about wanting to not make it too funny, which is that [I would] take out any sort of jokiness, but to play it straight and be real but at the same time he gave me permission to be a little rough around the edges and loose with my dialogue. So that I think the comedy comes from there, from his character, and who he is as a person, as opposed to any sort of knock-knock jokes.

What was sort of the toughest part of throwing yourself into this? You acknowledge this was different that what you’d previously done.

Certainly, there’s the challenge of all of the technical talk. I’m very quick to learn lines – it doesn’t take much time for me to read a sentence and know what I’m supposed to say or why I’m saying it. But when you’re talking about something where you truly have no knowledge, like the inner workings of a kaiju, then you really have to sort of study it and learn it. So unlike, say, playing Dale in Horrible Bosses, where I don’t have to learn what it’s like, or learn anything about a dentist’s office – you know, you sort of understand it – I had to be educated about these kaiju. And then Guillermo and I would have long talks about how he thought they worked and what they were made of, and what they were up to. The biology of them. So once I had all of that in my head, I was able to sort of throw it away a little bit, but there was a learning curve. And then it was a little bit more physical of a movie, the whole second act of the movie – I take a pretty serious beating. So there’s a chunk of the movie where I was being thrown to the ground or dragged around a lot, so it’s the only movie where I needed to stretch before I started acting.

At the same time, you have to be able to relate the experience of going through a kaiju’s memories. How tough was that stuff to imagine?

Guillermo made that very easy on me, where I never walked into a green room and then I had to stare up at a green box and imagine I was in peril. I would walk onto these elaborate sets, these incredibly detailed massive sets that Guillermo had built, and usually was stuffed with 500 screaming, crying extras, and people on bicycles, dogs running in the streets, chickens! And we would all be running and screaming and then sort of in the midst of all of that and maybe look at something, but by the time you’re in the middle of the take and all of that is going on, it’s very easy to sort of get in the moment. So he really made it easy on me in terms of the imagining aspect of the acting that you have to do. There were so many practical elements of the filmmaking that very often I didn’t have to do any of that. I was in a very real environment.

One of the hallmarks of your performances is this sort of mania, which you match with a real intelligence in this film. But are there times when you make a deliberate effort not to do that, or is your approach less cognitive and more intuitive?

Well, I don’t know to what extent it’s me being a slightly manic person, but I think it’s pretty much the situation that my characters are in in these movies. You know – I’m either being accused of murder or I’m going to be eaten by a kaiju, and I think there’s a certain amount of mania that’s necessary to make those scenes feel real. But who knows? I feel that’s an outsider observer’s opinion of what I am or I’m not doing. I think I’m always just trying to be me in the situation, so I guess if I was faced with a real crisis, I would probably get a little bit manic.

How strategic are you at this point about the roles that you’re choosing? And how much are you interested in tackling other genres as opposed to refining your work as a comedian?

Oh no, there’s definitely for me an impulse to do more than comedy. It’s been interesting and surprising how many people have come to me after this film and said how funny I am, and I’m like, I wasn’t really trying to be funny (laughs). But I just like good movies, and I’m as much a fan as I am a person in the movies, and hopefully we’ll be able to try other things – and if the audience goes with me on that, that would be fantastic. But there’s a little bit of a misconception, too, about how people get acting jobs. I’m really not there with a pile of seven million scripts and 900 directors waiting in line. The phone has to ring, and when the phone rings and someone says “we want you,” then you kind of have to weight what that project is. It doesn’t happen every day all day, you know; you need a Guillermo to come along and ask you to be in something. Or Seth Gordon in 'Horrible Bosses.' And Seth made those decisions easy. But occasionally there’s something you see and you say, okay, well, that’s not as good as these projects, or you just don’t see yourself doing it. But in terms of things I write, that’s a little different, because I do have the ability to write whatever I want. And were I to write a project for myself, I would stay primarily in the world of comedy, but I’m open to any kind of work that they will give me.