As for how much weight he lost? Murphy chose not to share a number, explaining, “Ach, no. I don’t want it to be, ‘Cillian lost x weight for the role.'”

Along with his physical transformation, the 47-year-old said the quick filming process allowed him to embrace the character much more.

“It’s like you’re on this fucking train that just bombs,” he told the outlet. “It’s bang, bang, bang, bang. You sleep for a few hours, you get up, you do it again. I was running with crazy energy; good because the character was like that. He never ate.

Oppenheimer hits theaters July 21.