SAN DIEGO, Calif. (AP) — While filming “Alien: Romulus,” Cailee Spaeny didn’t have to dig too deep to muster up sheer terror. She was often facing off against real creatures on set — or as close to real as they could get.

Under director Fede Álvarez, a prominent horror filmmaker, the actors played opposite animatronic and puppet alien creatures, including the famed “face huggers” and the dreaded xenomorph.

“From an acting standpoint, it’s such a gift because you’re not having to act against a tennis ball, so it’s right there. There’s less work you have to do,” Spaeny said in a recent interview.

Spaeny said using practical effects whenever possible was a priority for Álvarez from the beginning of the film’s production.

“It needed that kind of close encounter feeling of seeing that the actors are in the same environment with whatever’s the threat,” Álvarez, known for “Evil Dead” and “Don’t Breathe,” said. “It works not just for the audience, but for us, as well. When it comes to making the movie, it just makes everything way more complicated, but I think it makes for better movies.”

The lifelike creatures and commitment to practical effects proved to create a chilling final product — at least for those in the crowd at Comic-Con International, who were treated to some extended scenes and clips during a panel promoting the movie. The audience of over 6,000 people gasped and cheered during the scenes, which Álvarez said he edited deceptively to avoid spoilers ahead of the Aug. 16 theatrical release.

To accomplish the practical effects, Álvarez enlisted a team of filmmakers who have worked with the infamous Stan Winston, the special effects artist known for his work in the “Terminator” series, the first three “Jurassic Park” films and, of course, “Aliens.” Several of the behind-the-scenes creatives on “Romulus” have worked on previous “Alien” movies — including Ridley Scott, who is a producer on the upcoming movie.

“From a film lover’s standpoint, these guys — they’re responsible for some of the best creatures in Hollywood, so to have them around it sort of adds to the joy of what filmmaking and entertainment is all about. That was just a real treat,” Spaeny said. “I think it makes such a difference, not just for the actors and the crew making the movie, but hopefully for the audience, as well.”

Despite recruiting “Alien” alums behind the scenes, casting fresh actors who aren’t readily associated with larger-than-life characters was important to Álvarez. “Romulus” is nestled between “Alien” and its sequel, “Aliens,” but Álvarez has made clear that the new film is a standalone. He said he valued giving every audience member, regardless of whether they’ve seen any other “Alien” movies, a “full meal” as they watched “Romulus,” ensuring no one felt like they were missing any key details.

Still, as someone who grew up watching the “Alien” movies and admires the franchise deeply, Álvarez had to include some nods to his predecessors.

“When certain things happen that tie in with the other movies, if you’re an older audience, or even if you’re younger and you’re a fan and have seen all of them, you’ll get that pleasure of discovering and finding and connecting — and also sound like a smart ass next to your non-fan friend,” Álvarez continued.

With Álvarez’s eye for detail, cast member Isabela Merced said much of the production process was “meticulous,” down to the specks of fake blood on her face that had to be applied in the same exact spots for continuity. “It’s a perfect pattern,” she said.

As anticipation for “Alien: Romulus" grows and the response to clips at Comic-Con and online continues to be overwhelmingly positive, Álvarez said he and his collaborators are finally getting to feel their work paying off after the long creative process, which he calls “torture.”

“You do it for that audience. You do it to cherish that moment,” he said. “For me, to watch the movie that you made with an audience that is enjoying it is the biggest gift you can get.”

Spaeny said she hopes audiences will appreciate how “special” it is to watch a movie like this on a big screen.

“To get to sort of walk into a theater and have that experience with a group of strangers is one of the many beauties of movies.”