If there's something scary in the water, there's a good chance Alexandre Aja put it there. The horror auteur is arguably best known for his 2010 horror masterpiece, Piranha 3D, one of the most gloriously and disturbingly violent films ever made. His latest film, Crawl, strikes a decidedly more down-to-earth tone, trading the outrageously over-the-top spring break insanity of Piranha for a much more realistic and character-driven spin on the "scary monster in the water" genre.

Crawl was a surprise critical hit when it released earlier this year, and made a stellar $89 million at the worldwide box office, turning a tidy profit over its budget of $13.5 million. Critics praised Crawl for its visceral terror, strong character development, and outstanding production values, to say nothing of its magnificent portrayal of alligators hunting humans in the midst of an intense hurricane.

Related: Screen Rant's Crawl Review

During New York Comic Con 2019, Screen Rant sat down with Alexandre Aja to discuss the film, from its photorealistic CGI effects that brought the alligators to life, to developing a high-concept horror film with a small – but not tiny – budget. He talks about the differences and similarities between Piranha and the Sam Raimi-produced Crawl, and sheds some light on his fascination with the water (or, rather, the terrifying creatures that reside just beneath the surface).

Crawl is out now on Digital and On Demand, and Blu-ray.

Crawl poster alligator

This movie's really scary. When I was watching it, I was like, "I don't know how they did any of that." I didn't know what was animatronic, what was CGI... I mean, you couldn't have gotten a real alligator in there, that doesn't seem practical. How did you do it? Are they animatronics enhanced with CGI? Please, enlighten me!

It's fully CGI. Not only the alligators, but the hurricane, all the storms. We shot everything indoors. I'm really happy that the Blu ray is coming out. On the Blu ray, there is "behind the scenes" features, and I'm very proud about that. Just so people can understand what they are looking at, and how much we suffered for it.

Part of the reason I'm in this business is because I love movies and DVD special features, seeing the blue screens and all that stuff. So, when you watch a movie, you can generally piece together what's real, what's fake. But with this one? Nothing. I had no idea. And then I learned your budget was just $13 million.

I think we did good on the production standpoint. Our production value is very high, because we knew from the beginning that we couldn't do it in Florida. The story, of the hurricane and the wind, it's impossible. Every single tree would have to be replaced by CGI trees and then the rain, the water. It was clear that we had to build all of this. So we looked for a place where we could find the biggest warehouse possible to build these things. We knew we didn't need a soundstage. Because of the wind machines, the sound would have to be redone. We were really lucky to go to Belgrade, Serbia, to find a gigantic warehouse on the port of Belgrade. We built everything there. We had an amazing crew, a local crew. I think that's why we managed to stay within the budget. I mean, $13 million or $15 million is a really good budget. A lot of great movies can be done for that price. It's pretty much the sweet number that can afford you to do anything – if you know exactly what you're doing. If you're not going to waste any money, it gives you a lot of resources.

Right, you have enough to create, but not enough to waste.

For me, I was happy to find a studio that would back me up on this to make this movie. The problem we've had for so many years is that if you can do it for $15 million, you can do it for $5 million. That's not possible. A movie like Crawl could not be done for $5 million, in the Blumhouse type of budget. It needed that extra financial push to make it possible. I was scared, to be honest! We were working with this great company, Rodeo FX, based in Canada, for the visual effects. We shot during the summer, and then until Christmas, I was waiting. Just crossing my fingers to see the first fully finished alligator shot. When we got it, I was so relieved. I thought, this is amazing, this is gonna be so great. I thought, if we can get this quality on the 200 other shots, we're good!

That very first shot, where it bursts through the stairs, I 100% thought it was real. I'm still not over it. So, you have a workable, but still modest, budget. Are you huge on pre-vis?

No. I'm huge on script! I'm trying to really get the script to the place where I'm sure that there's nothing that's not going to end up in the movie. Then I do a lot of storyboards, just for the visual effects scenes. For this movie, it was pretty much every scene, but we didn't have the time to get storyboard artists to do the whole movie. We were shooting! So we just had to choose a few scenes. But by the end, you know how it's going to happen. What's important is, even if you shoot without the alligator, in every single shot, you have an element that shows you what will be there, what will be the size. So Kaya was amazing with that, and Barry as well. They were acting with stuntmen dressed in spandex suits, crawling towards them, or me holding a pole with a styrofoam head on the end, attacking them. I know it sounds super silly, and when you look at the behind the scenes, it looks silly as well! But without this, you don't have the reality of what's happening. Even for the camera movement, to know what a 15-foot alligator looks like on the lens, you need to have that reference. Then, when you're in post, you can add those elements.

We've had some alligator movies in the past, but I don't know if anything looks so realistic, not just in the photorealism of the CGI, but also in their movement, and the way they attack and take down their prey.

That's something that was very important for me. Studying the alligators and crocodiles, I realized how perfect they are in real life. They don't need to have an agenda for revenge, they don't need to have any type of other power to add to the story. They are just the most gnarly and vicious predator out there. The way they grab you and dismember you, the "death roll." The shark comes and cuts you clean. But the alligator, even with the pressure of its jaws, won't cut you clean. It will grab you and dismember you like a chicken bone. It's scary! I spent a lot of time studying all the best moments I could find on the internet. I watched hundreds of hours of alligator and crocodile footage from all documentaries and stuff. I tried to find the right moments to give to the animation team so they could really work. I think that helps give the feeling of fear, since it's actually trying to mirror the real world, real nature.

Kaya Scodelario in Crawl

Between Crawl and Piranha, your two best-known movies, they're both ten-out-of-ten masterpieces in my personal opinion... So my question is, what happened to you in the water as a child that traumatized you and inspired you to traumatize me and so many others?

(Laughs) I love the water. It's a weird thing, because I have no problem with water. I'm not scared of water. I was lucky to spend most of my vacations growing up in the water. But there's something that's...  It's like it's talking to you, directly to you. There's a connection, a very deep connection we have to the water, but sometimes it's scary. You cannot survive in the water, but at the same time, you feel like you are part of the water. It's a weird thing. I guess it's opened a lot of potential fear of what's underneath the water. And ourselves, we never see beyond the surface. Piranha was really about being on the side of the piranha. It was not really trying to be scary, but more like a fun extravaganza, a guilty pleasure, like "spring break under attack" kind of movie. But with Crawl, I really wanted to be with the characters and be scared about what's coming. Even the camera would try to be like the alligators, bobbing under, back and forth, having this kind of ambivalence within the water... I think it's just great... It's a pain in the ass! Trust me. When I did Piranha, I thought it was the most difficult movie I had ever made, because of the water. And then I had so much pleasure finishing the movie and seeing people enjoy it, I completely forgot. But then, the first day on Crawl, I remembered it. Altogether, it came back in a flash! Wow! What happened to me? Why didn't I think about that? Why am I in the water for ten hours a day for 40 days?! But I'm sure I'm going to forget and go back to the water again, at some point.

More: 10 Movies To Watch If You Liked Crawl

Crawl is out now on Digital and On Demand, and Blu-ray.