This week's terrifying sci-fi odyssey "Life," which stars Jake Gyllenhaal, Ryan Reynolds, and Rebecca Ferguson as crewmembers aboard a doomed international space station that comes in contact with a very nasty Martian (they nickname the squid-like beast "Calvin"), began, like the monster, as a simple, single-celled idea in the minds of writers Rhett Reese and Paul Wernick. The screenwriters, who have penned wise-ass classics like "Zombieland" and "Deadpool," take a surprisingly straightforward approach with "Life." This is a singularly scary movie. Prepare to clutch your significant other's hand until you hear bones break.

I got a chance to chat with them ahead of the film's world premiere at the SXSW Film Festival, and we talked about the inspiration for the movie, what it was like seeing their visions come to life (not only Calvin but the entire space station), the possibility of a sequel, and what's going on with "Deadpool 2."

Moviefone: What's interesting about this movie, especially coming from you guys, is how straightforward it is. Had you always wanted to do a straightforward sci-fi horror movie?

Rhett Reese: Absolutely. It really is. I grew up with a very active imagination, and movies like "Alien" and "The Shining" absolutely terrified me. When I was younger, I wouldn't even get to see them, but I'd see the commercials and they would absolutely terrify me. Deep down inside I always wanted to write something that was really scary. And this was the attempt to do that. We had fun. It was certainly not going for the same things we normally go for, so we got to flex a different writing muscle.

Technology seems to have freed you up, too. Because if you had been writing this 30 years ago there would have been no way to visualize something like this creature.

Paul Wernick: Absolutely. And not just the creature but the technology of the weightlessness and how that all visualized itself on screen and visual effects and wirework it's just ... We've been afforded so many gifts on this movie, with the ability to do stuff we couldn't have done even five years ago at the price point that we wanted to do it. And as for Calvin, he's a creature that we did extensive research on going into this. He's one of the seven main characters and the primary villain in the piece. We visualized him in a way that we tapped into research we did on the deep-sea world with these translucent sea creatures and the octopus was a great inspiration of ours. And then Daniel and the visual effects guys and the creature design guys brought it to life in a way that far exceeded even our expectations.

Was there ever a point where you guys said, "Screw it, let's give him a face"?

Reese: There was, at some point, because you're so used to seeing faces. But everybody felt that to anthropomorphize it too much would be a mistake. Because it really is based on the idea that it's all these interconnected cells that perform the bodily functions of all the differentiated tasks of a human body. So a cell that could be an eye cell and a muscle cell and a nerve cell all at once. It doesn't look as much like the average creature on Earth, let's say.

What was it like seeing the set for the first time?

Wernick: It was amazing. There's such detail, and I don't know if you know this, but it was shot on two soundstages at Shepperton in London, and they built basically the entire space station. The level of detail on everything, there was Russian on buttons that you'd never actually see on screen. The level and attention to detail was incredible and really awesome. It shows on screen. We could have shot this on the space station. It's pretty astonishing. And they had to build it in such a way that it had to be open air so the wires could move above it. It was a technological and artistic thing of beauty.

[Director] Daniel Espinosasaid the film is loaded with references to other movies.

Reese: I'm not sure what he's talking about.

Wernick: He might have put in some definite Easter eggs. There were some on "Deadpool" we didn't know about either. Everyone likes to throw stuff in there. I'm sure there's a bunch of stuff in this one. You know, "Alien" was definitely a huge inspiration of ours. It's a great movie, and almost 40 years ago it came out. For us it was making the thing as current and relevant and up to date as we could.

It also has such an international feel, which is really great in today's climate, with all of these countries working together. Was that something that you guys were cognizant of?

Reese: Yes, and that's the way the space station is, with astronauts from different countries aboard it. We didn't want to get into the divisiveness between nations or the divisiveness between characters in the sense that one character wants to bring the sample back to Earth to turn it into a weapon or something like that. We wanted a diverse but united crew that did their jobs well and had each other's back. That was part of the realism factor, with these astronauts putting aside their country's differences to come together on that space station to do work together.

Have you guys thought about a sequel to "Life"? The ending is terrific and definitely leaves the possibility for another film open.

Reese: Well, the sequel is going to be "Venom." [Laughs] We would love a sequel but it depends on whether or not people buy tickets.

Wernick: We always felt that an unconventional ending to a big tentpole movie would be cool, to us at least. We're always left-of-center and it felt left-of-center to us. But studios do love franchises so that set up the potential should the movie succeed, we'd love to make another one on Earth. It brings a smile to our face.Let's talk about "Deadpool 2." The first film was such a surprise for so many people. How do you do that again?

Reese: I think we'll find some more rules to break hopefully. I think sequels should have the familiar and the new in them. They shouldn't feel too similar to the previous movie otherwise people will get bored but I think they should also carryover in terms of tone and character so that people will still see what they know and love in the new movie. So we have similar elements, the tone will be the same, but the story is very different -- it'll have more characters, different characters, Deadpool is going to go on a new emotional journey so we want to keep it emotional. So it's all about striking that balance.

How did you guys feel about the movie hitting the way that it did?

Reese: It was probably the most gratifying moment of our careers. Because we've certainly reached big audiences but never a massive international audience like that, and the passion people had with it was so intense. We meet people all the time and the second you mention "Deadpool" they just light up. That, for us, is why we do it. There's that line in "Zombieland," when Woody Harrelson is gushing at Bill Murray and Bill says, "Well that's why we do it." That's what we say about "Deadpool." It's really fun.

Was it also fun introducing that character to the world?

Wernick: Well, there was always the fear that "Deadpool" was a one-quadrant movie. I think that's why it took six years to get made. And the fact that it extended all over age ranges, including kids as young as 10, which I cringe at, all the way to grandparents, to hit all four quadrants in a movie that could have, if it had gone wrong, was astonishing to us and really gratifying. Because it was a passion of ours, it remains a passion of ours. And to see that passion come across on screen and relay that to audiences is amazing and awesome for us.

Can you talk about working with new director David Leitch and what he brings?

Wernick: He's the best. His mind works in ways that others don't in terms of visualizing the action. We were just in the production offices and saw the pre-viz on one of the action scenes that we'd written and it elevated it in such a way that's jaw-dropping. So we're playing to his strengths and we feel like audiences are going to be blown away.

Reese: He also really gets the tone and the character. There was no learning curve. He came in and just got it.

So is it going to have more action?

Reese: I think it'll be a little bigger, just by virtue of it being a sequel and wanting to top ourselves. But we're not going to be lifting cities into the air or having alien invasions.

Wernick: We're saving that for the third one.

Reese: The first film was an underdog movie, and we don't want to feel like "The Avengers" -- that big and bloated and huge. It will always have a scrappy, underdog feel to it.

"Life" comes to our galaxy tomorrow.