The married creators of “Yellowjackets” always had big screenwriting dreams. Their idea about witchy teen cannibals struck the right alchemy.Ashley Lyle and Bart Nickerson share a marriage, a house in Los Angeles and a hit TV series that they created together. But not a computer screen, at least not when it comes to doing interviews.“We learned pretty early that one screen is not quite enough to contain us, gesture-wise,” said Nickerson, stationed in the living room. True enough, the creators of “Yellowjackets,” the second season of which began streaming on Friday (and airs Sunday on Showtime), both like to talk with their hands as they discuss the dark, witty psychological horror thriller that gave them their breakthrough after years of working in writers’ rooms for shows like “Narcos” and “Dispatches From Elsewhere.”They also like to share ideas, batting possibilities and pitches back and forth, exploring ideas that might have a chance of rising above the din. “One of those conversations just started around the idea of a girls’ soccer team being lost in the woods,” Lyle said from an upstairs room. Not a meditation on the hell of high school, or the futility of trying to outrun one’s past. This is Rule No. 1 in the Lyle-Nickerson book: Character and situation come first, laying the seedbed for themes and big ideas.“It’s not like we immediately started having conversations around trauma or female friendship,” Nickerson said. “We just started talking about characters and everything grew from there. At least that’s my story.”“I think that’s right,” Lyle confirmed from her post.Whatever the origin, the results have resonated. Showtime has already ordered a third season of “Yellowjackets” and signed the couple to an overall deal. Online discussions overflow with speculation about what might happen next or, sometimes, what the heck is going on now. The surviving members of that New Jersey high school soccer team — whose plane crashes en route to nationals in 1996 and who resort to doing very bad things to survive — have developed an ardent fan base.That those bad things appear to have involved some measure of witchcraft and, as the Season 2 premiere confirmed, cannibalism, is part of the appeal. Their creators, themselves native New Jerseyans who met in 2005 and shared a dream of screenwriting, are just happy they found an idea that stuck.“We’re constantly pitching things at each other, and I feel like 80 percent of the time the other person will go, ‘Huh,’” Lyle said. “And then 20 percent of the time or less, it’s like, ‘Ooh, save that one.’”“Yellowjackets,” it seems safe to say, was an “Ooh.”“I used to spend all day just living in fear of the night because that’s when my imagination was going to run wild,” Nickerson said.Ryan Pfluger for The New York TimesLyle, 43, and Nickerson, 44, met at a party given by a mutual friend in Jersey City. The theme was “beer Christmas”: Revelers drink beer from cans and then hang the cans from the Christmas tree. (The festivities continue: The friend now lives in Long Beach, Calif.; Lyle and Nickerson’s production company is called Beer Christmas.)They had heard about each other from other mutual friends, but Nickerson was usually busy helping his father with the family fast-food stand on the Jersey Shore, serving up burgers, hot dogs and sweet sausage sandwiches. “I was free labor all summer long,” he said.They were both outsiders of sorts. Lyle was a horror movie fiend; in eighth grade she was in a band that played Liz Phair and Sebadoh covers. (“Yellowjackets” boasts a killer ’90s indie-rock soundtrack.) Nickerson was a bit of a loner. “I never really found a thing or a group-level identity or a place to feel like I fit,” he said. “By the end of high school, I was just ready to get out of there.”After they finally met, realized they had shared aspirations, and fell in love, they did the natural thing: moved to Los Angeles with a suitcase full of spec scripts for various TV comedies, including “30 Rock,” “My Name Is Earl” and “The Office.” None were made. They wrote a one-hour pilot inspired by one of their favorite shows, “Veronica Mars.” Finally, their agents told them to write an original pilot and make it as weird as they wanted.In response, they wrote a high school murder mystery. It didn’t get picked up, but it helped them find their voice and generated that elusive commodity: industry buzz. Soon they were writing for the CW vampire series “The Originals,” and then the Netflix cartel drama “Narcos.” They were on their way.That they broke through with a witchy story involving cannibalism makes some sense. Lyle, who has an arm tattoo of a palm-reading chart (both are into tarot cards), recalled trying to convince a video-store clerk to rent her the cult horror favorite “Dr. Giggles.” She was 11. Nickerson was too freaked out by horror to give it a chance until he was older. His own mind was terror enough.“I used to spend all day just living in fear of the night because that’s when my imagination was going to run wild,” he said.Shauna (Sophie Nélisse, center, with Courtney Eaton, left, and Jasmin Savoy Brown) gets the cannibalism started in the Season 2 premiere by snacking on her dead friend’s frozen ear.Kailey Schwerman/ShowtimeMelanie Lynskey, who plays the adult Shauna, praised Lyle and Nickerson’s complementary qualities. “They’re such a good team,” she said.Kimberley French/ShowtimeThere’s enough fear to go around in “Yellowjackets,” which, for all its sensational qualities, explores truths that resonate more broadly. As they developed the idea, the creators took long walks though Griffith Park in Los Angeles, talking about the characters and what they mean to one another. Deeper themes emerged.“A lot of the thematics really just grew out of trying to put these people in scenarios together and looking at their relationships,” Lyle said. “It just became quickly apparent that it would be really complicated, in hopefully a great way.”Complication, of course, comes standard in high school relationships, even those that don’t involve witchcraft or cannibalism. Tawny Cypress, who plays the adult version of Taissa, a survivor who grows up to become a state senator, described the story as universal. Her character experiences a frightening form of dissociative identity disorder, and winds up sacrificing the family dog in a cultish ritual. But less extreme versions of life can still be terrifying.“High school sucked for everybody,” Cypress said in a video call. “Nobody came out unscathed, and we carry that around with us still. These girls had a much bigger experience, but we all are stuck with things that formed us back then.”Karyn Kusama, an executive producer on the series and an accomplished film director (“Girlfight,” “Destroyer”), was even more specific.“This idea of girls feeling they need to destroy each other in order to survive felt very emotionally familiar to me,” she said in a video call. “I just thought it was an interesting thing to explore in real terms, and then allow the metaphor to be quite powerful and clean while the narrative event is extremely messy.”Season 1 hinted at the most extreme expression of that metaphor, a taboo subject that never really came to fruition: cannibalism. The pilot all but promised it, to the point that viewers might have fairly wondered: Who will be eaten? When? By whom? And is there hot sauce?“I don’t think people will be disappointed this season,” Lyle said in reference to the cannibalism teased by the first season of “Yellowjackets.” The Season 2 premiere has already begun to deliver. Ryan Pfluger for The New York TimesNickerson sounded a little sheepish about what he called the first season’s “lack of cannibalism.” But he swore they weren’t teasing. (They have since confirmed in interviews that the girls would eventually get their fill, and the Season 2 premiere gets things started when Shauna, played as a teen by Sophie Nélisse, makes a frozen snack of her dead best friend’s ear.)“It wasn’t that we set out to be like, ‘Well, there will be no cannibalism in the first season,’” he said. “It was more that it didn’t feel like we had gotten the characters to a place where that would feel organic. We wanted viewers to be with them as much as possible to make this seem like not a salacious choice, but the only choice.”Lyle added: “I don’t think people will be disappointed this season.”Lyle and Nickerson didn’t quite finish each other’s sentences when we spoke. But they came pretty close, glossing and elaborating on a point here, gently correcting there. It’s not all fun and games when they work at home, but they appear to complement each other in productive ways.Melanie Lynskey, who earned an Emmy nomination for her performance as Adult Shauna, said she saw a definite pattern in the couple’s creative relationship.“Ashley’s so funny and so quick and kind of gathers her thoughts in a very businesslike way,” she said by phone. “And Bart is more emotional; he takes a minute to get to the thing. But along the way, there are all these great stop-offs, and they’re such a good team.”Cypress, a fellow New Jerseyan, was more succinct about the couple: “I [expletive] love those weirdos.” More