To fully achieve the look of J. Robert Oppenheimer, the scientist behind the atomic bomb, Oppenheimer lead actor Cillian Murphy went on an extreme diet—the details of which his co-star Emily Blunt recently shared with Extra. “He had such a monumental undertaking. And he could only eat, like, an almond every day,” she claimed. “He was so emaciated.” Murphy previously told The New York Times that he wanted to embody Oppenheimer’s “very distinct physicality and silhouette” and was pushed by director Christopher Nolan to “be immersed in the essence so strongly.” Murphy explained: “I had to lose quite a bit of weight, and we worked with the costume and tailoring; he was very slim, almost emaciated, existed on martinis and cigarettes. He had these really bright eyes and I wanted to give him this wide-eyed look.” However, the Oppenheimer star has warned of the dangers of shedding so much weight for a role. “You become competitive with yourself a little bit which is not healthy,” Murphy told IndieWire. “I don’t advise it.”