M. Night Shyamalan on one of the most 'grotesque' scenes he's directed

By his own admission, M. Night Shyamalan's summertime sleeper hit, Old, was heavily inspired by Peter Weir's 1975 cult favorite Picnic at Hanging Rock. "You're dead on," the celebrated filmmaker and two-time MVP of Horror tells Yahoo Entertainment when we noted the connection between the two movies. "Picnic at Hanging Rock was a huge inspiration."

But when it came time to stage Old's centerpiece sequence — a harrowing childbirth scene — Shyamalan turned to the mother of all pregnancy-themed horror movies: Roman Polanski's Rosemary's Baby. "That's one of the greats for me," he says of the 1968 classic, which stars Mia Farrow as a woman who fears, for good reason, that she's going to give birth to the spawn of Satan.

There are no devil children running around the remote tropical beach that serves as the setting for Old. But something decidedly wicked happens to anyone who sets foot on those sandy shores. The vacationers at the center of Shyamalan's story are shocked to discover that they're suddenly living their lives in fast-forward: Every thirty minutes, they age another year. Within a matter of hours, thirtysomething married couple Guy and Prisca (Gael García Bernal and Vicky Krieps) are pushing 60, and their young kids, Trent and Maddox, are zipping through their teenage years and headed for their twenties.

In the midst of his tumultuous teens, Trent (Alex Wolff) develops feelings for fellow rapid-ager, Kara (Eliza Sanclen). Within an hour, she's pregnant and ready to give birth, but her still-youthful mind can't process what's happening to her radically transformed body. And everyone else on the beach is just as freaked out as Kara. "The idea was that it's first almost like dark comedy," Shyamalan says of how the scene begins. "And then it starts to become warped and grotesque. I mean, every single character loses their mind by the end of that sequence!"

Not wanting to break the tension of the scene, Shyamalan captured it in one long take, with the camera in near-constant motion. And the ensemble cast performed like a theater troupe, staying in character until he finally called cut. Shyamalan even had the cast rehearse the scene long before they filmed it, working on weekends to practice the choreography and moving in concert with his camera. "When they were finished [shooting it], they were done," the filmmaker says, laughing. "They didn't even get up off the sand! They had really gone to insanity by the end. It was really powerful, acknowledging a child, having a child and all the dark things that happen afterwards."

Shyamalan credits Scanlan with bringing additional nuance to the scene that he wouldn't necessarily have. "She's an amazing actress and was full-on the whole time. She wore the prosthetic [belly] a lot [while] walking around, and her back would ache. She's one of those actresses that gets totally into it, so we followed her lead. Whatever she was doing, we just bounced off of it."

Old's delivery scene might seem mild when placed alongside the graphic depictions of pregnancy seen in horror movies like the infamous 2007 French film Inside. But gory scares have never been part of Shyamalan's toolkit, going all the way back to his breakout ghost story, The Sixth Sense. And the director says he never imagined breaking that tradition for Old.

"My instincts are always to insinuate: You can imagine much worse than I can show you. I just need to ignite your imagination a bit. I love that part of the genre... and the great versions [of that] — like the original Invasion of the Body Snatchers — stay with us so much more. When I can make you not a passive viewer, it stays with you."

— Video produced by Kat Vasquez and edited by Luis Saenz

Watch the trailer:

Old is currently available on most VOD services including Amazon Prime Video.