Shooting Best Picture nominee “1917” was no easy task.

On the red carpet at the Oscars, stars George McKay and Dean Charles Chapman talked about the gruelling shoot for the film and the guiding light director Sam Mendes provided for them on the project.

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Describing the difficult conditions shooting the film’a No Man’s Land sequence, Chapman said, “The mud is equivalent to walking on ice, that’s how slippy it was.”

McKay talked about the moment later in the film when his character is running through a battle and falls over, but gets up and keeps on going.

Explaining that his fall was unrehearsed, he said, “The rule always was, ‘Unless Sam says stop, you don’t stop, so I just got back up and carried on running.”

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“1917” is strongly predicted to win big at the Oscars on Sunday night, which led to a funny mishap earlier in the day.

The Instagram page for the upcoming Broadway play The Lehman Trilogy, directed by Mendes, accidentally boasted that he had already won Best Picture and Director for the acclaimed war film.

According to a screenshot obtained by TMZ, the ad ran for several hours on Sunday, prior to the Academy Awards.

A spokesperson for the play told¬†TMZ that the ad was posted by mistake, and while the team are all pulling for “1917” to win, they do not yet know the results.

The Lehman Trilogy opens March 26, with previews beginning March 7.