Jason Issacs told a funny story about this at DST 2018 about that scene they shot when they were in "hell". Apparently, they got some sadists together and told them to have fun for a few minutes while someone films them. Jason said the cameraman was all white afterward, thinking that he just came back from Vietnam or something. 
He also said that on opening day, he and a few others snuck into a cinema to see how well the movie was doing, which was a bad idea because it bombed and all the screens were near empty.

He also said that on opening day, he and a few others snuck into a cinema to see how well the movie was doing, which was a bad idea because it bombed and all the screens were near empty.