It is the evening before the London premiere of the keenly anticipated film The Thing With Feathers. Max Porter, author of the novella on which it is based, and Benedict Cumberbatch, its star, are, rather unexpectedly, chatting about Dwayne Johnson – aka the Rock – in The Smashing Machine, Benny Safdie’s bruising biopic of the MMA pioneer Mark Kerr.

Johnson “was saying at the junket that it’s the first time he didn’t think about box office”, Porter says. “A lot of people called bullshit. But, actually, I don’t ever think about the box office.

“I think about collaboration. Think about the relationship you have with the person you’re sitting with in a room, saying, ‘Here’s a way of doing this character on screen.’ Deal with that. Then I meet Benedict and talk to him about the relationship he’s going to have with his character.”

“Hang on,” Cumberbatch says. “Let’s go back to the Rock for a minute, because I don’t think it’s complete bullsh*t. He’s so locked into an extraordinarily successful business relationship with the entertainment industry.

“And this is the first time he’s saying, ‘Actually, for me, this is about the challenge of doing something I’m frightened of. I’m not smiling at the press and doing my routine, I’m doing character work.’”

Cumberbatch, an actor of looming presence, has shared bodies with a sorcerer in Doctor Strange, breathed fire into The Hobbit’s dragon Smaug and squared up to Andrew Scott’s Moriarty in Sherlock. But none of these experiences prepared him for scenes playing opposite a man-sized crow in The Thing With Feathers.

His unnerving scene partner in the film adaptation of Porter’s book Grief Is the Thing With Feathers – a project Cumberbatch also executive produced – was the product of animatronics, the physical performance of the acto