Sisters Rooney and Kate Mara had to talk in sync with each other for Werner Herzog’s drama “Bucking Fastard,” revealing the challenge was “surprisingly” easy for them.

The film follows two siblings who are so close they “speak in unison, love the same man, and have the same dreams,” according to the synopsis. It was directed by Werner Herzog, the influential German filmmaker of “Nosferatu the Vampyre” and “Aguirre, Wrath of God.”

“At first, it was very daunting, the idea that we were going to be playing this kind of same person,” Rooney said at a Venice Film Festival press conference ahead of the movie’s premiere on Thursday. “But I think we found pretty quickly that having a lifetime together and all this history and a childhood of playing together. There was just an unspoken world between us that we didn’t have to work very hard to create at all. I’ve never laughed so much, it was a very once in a lifetime, unique experience.”

Kate added that speaking in synchronicity “felt almost like a song.”

“We had this unspoken sort of rhythm together,” she said. “It was very musical. It sort of happened quite naturally. Surprisingly, it came with a lot more ease than we were expecting.”