Lone Survivor director Peter Berg has revealed how he had to physically stop his actors from doing their own stunts.
The filmmaker behind the US war drama admitted he once had to run up a mountain to restrain Ben Foster from trying out a risky move.
"I would be off shooting something else and I would hear that Ben Foster had snuck up onto the mountain and was going to try. I ran up there and went, 'Ben, you can't do it'," he recalled.
Peter said his cast, including Ben, Mark Wahlberg and Taylor Kitsch, were keen to do more action work than they were allowed, because it was too dangerous.
"They all did some, but not as much as they wanted to. We hurt a couple of stuntmen early on so my job became slowing it all down because everybody wanted to do a great job for Marcus. So t here are shots of them falling off pretty steep cliffs, but it's less than they wanted," he continued.
The actors became a "band of brothers" after embarking on a training camp with real-life Navy SEAL Marcus Luttrell, whose memoir the film is based on.
"The most important quality I was looking for in all of them, besides being physically fit and looking capable, was they had to be willing to roll up their sleeves, go into that culture, do that training camp and learn. These actors wanted to do that very badly," Peter said.
"Ben and Mark had worked together on Contraband so they knew and liked each other, but by the time they came off that mountain, it was... like (they were) one big actor. They were very close and I think they formed friendships that will last forever."
:: Lone Survivor is in cinemas now.