Christopher Nolan says the shocking 'Oppenheimer' line about why America shouldn't bomb Kyoto was improvised: 'No one in the room' knew 'how to react'

• Christopher Nolan said that the most chilling line in "Oppenheimer" was a last-minute addition.

• He told The New York Times that actor James Remar found out his character honeymooned in Kyoto.

• He said it resulted in "a fantastically exciting moment where no one in the room knows how to react."

Christopher Nolan has said that the most chilling line in "Oppenheimer" was actually a last-minute addition suggested to him on the day of filming.

While Nolan penned the entire script for the epic three-hour movie alone, he revealed in an interview with The New York Times that there was one small improvised moment from a cast member that was too good to leave out of the final cut.

The Academy Award-nominated director said that James Remar came up with the nauseating moment in which his character, Henry L. Stimson, says that they should strike Kyoto off a list of possible bombing locations in Japan because it's a "beautiful" city where he and his wife honeymooned.

Nolan recalled that Remar "kept talking to me about how he learned that Stimson and his wife had honeymooned in Kyoto" after doing his own research into the then-Secretary of War.

Remar explained to him "that was one of the reasons that Stimson took Kyoto off the list to be bombed," said Nolan.

Nolan had initially written Stimson "crossing the city off the list because of its cultural significance," but the filmmaker told Remar to "just add" the additional line about honeymooning in Kyoto.

"It's a fantastically exciting moment where no one in the room knows how to react," Nolan added.

"Each actor was coming to the table with research about what their real-life counterpart had been," Nolan said elsewhere in the interview. "They had tons of homework to do."

"They had a great resource with 'American Prometheus,'" he said referencing the book the movie is heavily based on, "American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer" by Kai Bird and Martin J. Sherwin.

Nolan said the cast's own research meant that the director was able to do something he'd "ever really been able to do in the past" and create a more realistic backdrop.

"So, for example, with the scene in the section classroom with all the scientists, we would be able to improvise the discussion," he explained. "The script is there, but they could come into it with passion and knowledge based on all of their own learning."

Remar wasn't the only cast member to dig deeper to research his character.

Cillian Murphy, who portrays the titular nuclear scientist, told the Guardian in July that he didn't just want to act like Oppenheimer. He asked science advisors to help him think like him, too.

As previously reported, in order to portray the genius accurately, Murphy met with Kip Thorne, a Nobel prize-winning theoretical physicist, and David Saltzberg, a professor of physics and astronomy.

"He had very interesting questions, probing and trying to gather information to help himself playing this role. And I was very impressed," Thorne told Insider.

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