Benedict Cumberbatch says the 'most painful thing' while shooting 'The Power of the Dog' was pretending he knew how to play the banjo

• Benedict Cumberbatch called pretending to play banjo "most painful thing" on "The Power of the Dog."
• He said it was "stupid" to try to master the instrument in only four weeks.

Benedict Cumberbatch said the "most painful thing" about starring in "The Power of the Dog" was pretending to know how to play the banjo.

Cumberbatch plays Phil Burbank in the Jane Campion-directed Western, which is out in select theaters on November 17 and streaming on Netflix starting December 1. The actor opened up about getting into character for the intimidating ranch head at a panel on Thursday at the TCL Chinese Theater alongside Campion and costar Kirsten Dunst.

While Cumberbatch called the scenes where Phil is nude onscreen "interesting," he said it was "painful" to pretend to play the banjo.

"[My character] is someone who has done it all their life, and I'm trying to master it in four weeks or something stupid. That's tough," Cumberbatch told the audience, according to The Hollywood Reporter.

Cumberbatch also told Esquire in a profile published on Wednesday that he wanted to become "world class at the banjo" while working on the film, but he hasn't made much progress.

"I'm very much not. I'm very far off," he said.

Cumberbatch also told Esquire that he stayed in character as the Montana ranch owner for the entire shoot.

This included only responding to "Phil" instead of "Benedict" and smoking cigarettes "perfectly rolled with one hand" as his chain-smoking character would.

"That was really hard," Cumberbatch told Esquire. "Filterless rollies, just take after take after take. I gave myself nicotine poisoning three times. When you have to smoke a lot, it genuinely is horrible."

In addition to giving himself nicotine poisoning - which can cause nausea, vomiting, and extreme fatigue - he also said he went days without showering to add a "layer of stink" to himself like Phil.

"I wanted people in the room to know what I smelt like. It was hard, though. It wasn't just in rehearsals. I was going out to eat and meet friends of Jane and stuff. I was a bit embarrassed by the cleaner, in the place I was living," he said.