Benny Safdie grew bushy eyebrows for 'Oppenheimer'.

The 37-year-old plays the Hungarian-American physicist Edward Teller in Christopher Nolan's blockbuster and explained how the director encouraged him not to pluck his brows so he could resemble his alter ego.

Benny told Vulture: "I am proud to say that it's all my eyebrows. Teller had the best eyebrows.

"Every once in a while I have a straggler that I'll just pluck out, cause it looks a little too crazy. But Chris said, 'Don't do that. Let's just let it go crazy.'

"I had the most insane eyebrows for months and months, and you just had to brush them out and then they shined in all their glory."

Teller spoke with a thick Hungarian accent and Benny explained that the toughest element of the part was to mimic the voice of his character.

The 'Licorice Pizza' star recalled: "The accent was something I was so nervous about.

"I remember Chris asking me, 'How's the accent coming?' And I'm just like, 'Oh my God, how am I going to accomplish this?'

"I didn't know if he was going to want me to do it. But he sent me all of these interviews and we talked about how Teller speaks and who he is. It was a long process of working together to really nail it down."

Benny added: "I remember finally I was like, 'You know what? I could sound crazy, but I don't care. This is what Teller sounds like and I'm just going to do it.'

"I sent a voice memo where I just narrated what my breakfast was and how Teller really liked pineapple."