When it came time to cast his supernatural horror film "Mama," Guillermo Del Toro knew he wanted "Zero Dark Thirty" star Jessica Chastain for the lead role - despite the fact that no one knew who she was yet.

"Back in the day, Jessica Chastain was not well known," said Del Toro, sitting down with me recently to discuss the upcoming scare flick. "But she was already very prestigious and very choosy about what she wanted to do. So I started a very, very slow, prolonged courtship of her manager, her agent...and finally I got to meet Jessica, who loved the screenplay. She said 'Look, I love the character, it's a different color for me.' And we came out of that meeting with her understanding how a movie like this could be great for an actor."

While it's important to note that Del Toro didn't actually direct the new film (that task fell to newcomer Andres Muschietti, who also helmed the short on which the movie was based), as one of the project's producers he played an active role throughout its journey to the screen, from development to post-production. At a certain point he even attempted to talk Muschietti out of using one particularly expensive special effect - a terrifying and highly effective bit that involves two feral young girls scampering about an abandoned house on all fours. But Muschietti wouldn't budge, and the result was something that ultimately worked to the film's advantage.

"This is something Andy really fought for," said Del Toro. "It was a very expensive effect. We needed to use digital doubles for them, and everybody kept arguing, 'you don't need it, you don't need it' - including me. I kept telling Andy 'are you sure you don't wanna...?' and he said, 'I need it, absolutely.' And we made the room for him to make the effect and it's very effective, very good."


Care to hear more? Click on the video above for the full interview, in which Del Toro also discusses his upcoming projects, including the haunted house horror flick "Crimson Peak," his TV series adaptation of "The Strain" and that brewing "Pacific Rim" sequel.

"Mama" hits theaters on January 18.

Official synopsis:

Guillermo del Toro presents "Mama," a supernatural thriller that tells the haunting tale of two little girls who disappeared into the woods the day that their parents were killed. When they are rescued years later and begin a new life, they find that someone or something still wants to come tuck them in at night.

Five years ago, sisters Victoria and Lilly vanished from their suburban neighborhood without a trace. Since then, their Uncle Lucas (Nikolaj Coster-Waldau) and his girlfriend, Annabel (Jessica Chastain), have been madly searching for them. But when, incredibly, the kids are found alive in a decrepit cabin, the couple wonders if the girls are the only guests they have welcomed into their home.

As Annabel tries to introduce the children to a normal life, she grows convinced of an evil presence in their house. Are the sisters experiencing traumatic stress, or is a ghost coming to visit them? How did the broken girls survive those years all alone? As she answers these disturbing questions, the new mother will find that the whispers she hears at bedtime are coming from the lips of a deadly presence.