Months into rehearsing for the new twist-filled drama “Parallel Mothers,” Penelope Cruz could feel her maternal instincts taking over.

The Oscar-winning actress plays a single mom with a massive secret in the Spanish film, and embraced the challenge of immersing herself in the complex role.

“When we were rehearsing with a doll, and somebody from props would come and try to get the doll just so that I would rest ... I would react like a lioness, like an animal. Like, ‘Don’t take the doll from me,’” Cruz recalled.

“I was not planning to react like that, but I like when those things happen,” said Cruz, who has two kids with actor Javier Bardem. “It means something about (how) the process has really taken over.”

Cruz stars in “Parallel Mothers,” now playing in theaters, as a photographer named Janis who becomes pregnant early on in the film.

Janis is assigned a hospital room with a young woman, Ana, who is also expecting a child. Their lives quickly become intertwined, kicking off a complicated journey filled with drama.

“Something happens in that hospital that is going to bond their lives forever in very peculiar ways,” Cruz, 47, said. “Then my character is faced with huge moral dilemmas. She has to make very difficult decisions. She has so many problems. She is a good person, but she also knows how to lie in life very well.”

The Spanish-language film is written and directed by Pedro Almodovar, whom Cruz has frequently worked with throughout her career. Previous collaborations include 1999′s “All About My Mother,” which won an Academy Award for best foreign language film, and 2006′s “Volver,” which earned Cruz a best actress nomination.

They spent four months rehearsing for “Parallel Mothers,” which Cruz says required maximum concentration and effort from the entire cast and crew to meet Almodovar’s high standards.

“I just love this profession,” Cruz said. “I’ve loved acting since I was a little girl. You’re always a student, and you never get to a place where you feel, ‘Oh, now I have this under control.’ That will never happen. Every movie is starting from zero in a way, because you’re going to get to live with this new person for a while, and get to really know that person, or try.”

The film features a secondary plot in which Cruz’s character works to track down the remains of her great-grandfather, who died during the Spanish civil war, to provide closure for her grandmother.

“It’s great that Pedro’s talking about something like that, because his movies travel everywhere,” said Cruz, who won the best supporting actress Oscar for “Vicky Cristina Barcelona” in 2009.

“This is something that is not only a problem of our country. So many places in the world can identify with that.”

Cruz was named best actress at the Venice International Film Festival for “Parallel Mothers” after the movie premiered there in September. She received the equivalent honor from the Los Angeles Film Critics Association this month.

She appreciates how Almodovar never judges any of his characters, and said she couldn’t judge Janis, either.

“Everybody is like, ‘Oh, I’m asking myself, what would I do?’” Cruz said. “That’s what I love about the movie, that everyone can ask themselves those questions, and understand that whatever she would have done, I think the audience would at least understand.”

If you go

PARALLEL MOTHERS

R, 123 minutes

Playing at Niantic Cinemas