How did a cat named Schnitzel win the starring role of Frodo in “A Quiet Place: Day One”? He impressed director Michael Sarnoski with his nonchalant confidence, rugged looks and intelligent face.

“He had a lot going on behind his eyes,” Sarnoski said in an interview last week, when the film made its theatrical debut. “A lot of the other cats were really adorable but almost too cutesy, like they would be in a cat food commercial. And Schnitzel had a little bit of an edge, like you could kind of believe he was a bit of a world-weary street cat.”

Frodo has a lot to be weary about in this cinematic universe. The film, a prequel to the 2018 horror movie “A Quiet Place” and its 2021 sequel, chronicles aliens invading Earth and attacking everything that makes a sound.

Lupita Nyong’o plays Sam, a cancer patient caught in the apocalypse with her service cat while visiting New York. Although most people want to escape Manhattan, Sam knows she is dying regardless and just wants to go to Harlem, where she grew up, and grab a slice of pizza. She meets a British law student named Eric (Joseph Quinn), who agrees to join her, and the cat becomes a comfort to them both. (Sam is a poet, hence Frodo’s literary name.) And spoiler warning: Audiences will be happy to know Frodo makes it out alive.

Sarnoski, who also wrote the screenplay, grew up with cats and knew he wanted Sam to have an animal companion. But the creature would need to be able to navigate an urban apocalypse in silence. A dog would bark at a threat, and something like a bunny, say, wouldn’t fit in the grit of Manhattan. But it’s common to see cats around the city, wandering the streets or guarding delis. Frodo even meets a bodega cat, played by a ginger-and-white shorthair named Stanlee, a runner-up for the lead role.

“A lot of people are like, ‘Why doesn’t the cat make more noise?’ But cats are very smart, predatory creatures,” Sarnoski said, adding that he believed a cat would recognize the danger and figure out how to survive. “I figured a cat would have a shot.”

The film’s budget included a computer-generated cat, but Sarnoski was dedicated to using the real thing. “I think it makes you feel more connected,” he said. “And you feel like they are a real character more.”

Schnitzel, who was previously in “The Marvels,” was one of several cats from the training company Birds & Animals U.K. who auditioned, which consisted of roaming around and just doing cat stuff. After Sarnoski settled on Schnitzel, another cat, Nico, whom Schnitzel has known since kittenhood, was also booked. His all-white fur was colored with a semi-permanent, animal-friendly dye to match Schnitzel’s distinctive black-and-white markings.

“Schnitzel knew he was the hero cat,” Sarnoski said, adding that he was the “diva” used for many of the close-ups. “Nico was a little more like, ‘Yeah, I’ll do what I gotta do.’ He was sort of like a stunt double.” A stuffed version (deemed Frida) was used for scenes with more action.

The trainer, Jo Vaughan, had about 12 weeks to prep the cats. A significant portion was spent familiarizing them with being carried and walking on leashes. “If there’s two things cats don’t like,” Vaughan said, “one is being on a harness and lead, and two is being carried.”

The cats weren’t the only ones who had to adapt to something they didn’t like: When filming began, Nyong’o, who won an Oscar in 2014 for her role in “12 Years a Slave,” was afraid of the creatures. Sarnoski said she spent about an hour before shooting each day doing “cat time” to get to know Schnitzel and Nico.

Still, no matter their training, which also consisted of practicing water scenes in a pool designed for dogs, the cats decided what they were, and were not, willing to do. While shooting a scene set in a flooded subway station in a water tank, Sarnoski said, one of the cats bailed from its makeshift raft. “Joe Quinn, I think, was the one that swam to the cat and was like, ‘We’ll get you out,’” he said. Another challenge was capturing a cat when the camera was in motion. “If you’re on a Steadicam following the cat,” Sarnoski said, “the cat’s always going to be like, ‘What is that thing behind me?’”

Frodo remains catlike throughout the film, occasionally becoming distracted and wandering off. But he comes to represent the human characters’ desire to protect one another. As a service cat, he offers Sam solace and provides it for the audience as well. It’s easy to see why Nyong’o ultimately became a cat person, cuddling her furry co-stars.

Once filming wrapped, and Nyong’o had to part with Schnitzel and Nico, she adopted a cat, who is orange and named Yoyo. “Everyone should have a cat,” Sarnoski said. He ended up getting one, too.