This was how Swedish actress Noomi Rapace pitched her team on doing a new movie called “Lamb”: “OK, I’m going to do this very small Icelandic film with a first-time director, there’s no money and there’s like a human lamb baby, sort of.” This was their (understandable) response: “Wait, what?”

As strange as it might sound, the supernatural folktale/family drama “Lamb” (in theaters now) became “one of my dream projects ever,” says Rapace, who plays adopted mother to a hybrid sheep girl. And even though there’s that old Hollywood adage to never work with children or animals, director/co-writer Valdimar Jóhannsson used both to create the most visually arresting character in an intriguing film about parenthood and man vs. nature that’s destined to be a conversation starter. “Lamb” centers on Maria (Rapace) and Ingvar (Hilmir Snær Guðnason), a sheep-farming couple in rural Iceland who’ve recently lost a child. One day, an unusual creature is born in their barn and they take it in to raise as their own. Calling their new “daughter” Ada, they find renewed joy, though they’re visited by Ingvar’s brother Pétur (Björn Hlynur Haraldsson), a black sheep of sorts who questions his sibling’s decision. Not to mention the various forces of nature – including one very ticked-off mama ewe – create overwhelming tension in the couple’s lives. Maria is “trapped in almost a limbo reality in the beginning,” Rapace says. “Her heart is put on hold because it’s kind of impossible to recover from losing a child. She’s just getting on with her life and then she’s given this beautiful opportunity to be a mother again. Or maybe she just takes it. But how she balances between extreme fragility and strength and rage and this primal, almost violent side, that combined with the visual (look of Ada) was just for me mind-blowing.”

On Rapace’s first day, she was delivering real baby lambs for a few of the movie’s key early scenes. “The physicality really placed me right into the story,” says Rapace, who grew up in Iceland and did “a lot of heavy farm work” as a youngster. (One Icelandic farmer gave her lamb-delivering skills a stellar review, her director Jóhannsson reports: “He was saying it was like Noomi had been doing it forever.”) There were a bunch of animals on the farm where cast and crew lived and worked. Carlos the cat, who plays Maria and Ingvar’s persnickety pet, was “the biggest diva,” Rapace says. “It was his house and he felt like we were intruders.” But Ada, who quickly grows from baby to toddler during the film, was the result of a team effort involving one lamb, nine human children, two puppeteers and a bunch of visual effects. The lamb who played Ada was “very small and handy in the beginning,” Rapace says. “You could just hold her.” They filmed “Lamb” in two different time frames, however, and by the second block of production Ada had grown to around 70 to 80 pounds: “It’s a big baby,” Rapace admits, adding that the lamb became attached to them, as did the kids. Some of the children “were easier to work with and some were more strong-minded and wild but they were also growing.”

Rapace, who has a teenage son, began to feel maternal about Ada halfway through filming. “I forgot that she was not real,” she says. “I totally feel like Maria took over my system and I became the mother of Ada. It was intense.” The actress recalls one “divine moment” where Maria puts a flower crown on Ada’s head: Rapace was up close to the usually squirming young sheep’s face “and all of a sudden she just became so still and we got this really powerful connection. We started breathing each other’s air. It felt like we had a secret language.” As the on-screen Ada grows and gets more mobile and social like a real kid, Jóhannsson maintained a constant balance between human and animal. For example, Ada understands what her parents are saying but doesn’t communicate back the same way. In early iterations of the script, “she was talking a lot,” the filmmaker says. “But then we just realized that she should not speak. Somehow we felt that would make her stronger.” Since debuting “Lamb” at Cannes in July, Rapace and Jóhannsson have attended screenings and Q&As where people dressed up as lambs. They’ve also had heated conversations and discussions about the movie’s themes.

“My favorite movies are the ones that are not so straightforward,” Rapace says. “It has the simplicity to it, but it’s like a volcano underneath. I would love people to allow themselves to be totally impolite and just have their own take on it. And if they don’t like it, that’s fine, too, but I love that it evokes emotions.”