Oppenheimer's Cillian Murphy says he was subjected to "chemistry tests" with Florence Pugh before prolonged nudity scenes.
The film is one of this year's most hyped movies, which is set to include "prolonged nudity".
Murphy plays nuclear scientist J Robert Oppenheimer who gets in a relationship with psychiatrist and physician Jean Tatlock, played by Pugh.
The actor said he has been under instructions to not give too much away about the upcoming film but has revealed he had to go through chemistry tests with Pugh and Emily Blunt.
Despite undergoing the "tests", Murphy said he found the process "outrageously silly".
Speaking to The Guardian, Murphy said: "They put two actors in a room to see if there’s any spark, and have all the producers and director at a table watching.
"I don’t know what metric they use, and it seems so outrageously silly, but sometimes you get a chemistry and nobody knows why."
The film, directed by Christopher Nolan, is also set to include nude scenes between Murphy and Pugh, which makes it one of Nolan's rare films to include sex and relationships plotlines.
Oppenheimer is the first of Nolan's films since Insomnia (2002) to receive an R rating in the US.
An R rating is the equivalent to a 15 rating in the UK but age ratings for any one film vary depending on the discretion of each country’s ratings bodies.
Oppenheimer received its R rating for "some sexuality, nudity, and language", while in the UK it received a 15 rating for "strong language and sex".
The movie is set to feature an all-star cast including: Matt Damon, Robert Downey Jr, Rami Malek, Gary Oldman, Dane DeHaan, Josh Hartnett, Kenneth Branagh, Matthew Modine, Casey Affleck, Alden Ehrenreich, and Jason Clarke.
Oppenheimer is released in cinemas on July 21 which is the same day as Greta Gerwig’s Barbie.
However some fans won't have to decide which film to see as a trend has gone viral dubbed "Barbenheimer" where movie buffs are set to see the new released back to back.
The trend has become so popular that Murphy, Margot Robbie and Tom Cruise have publicly supported it.
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