John Krasinski ran through a real fire on the set of '13 Hours: The Secret Soldiers of Benghazi.'
The 36-year-old actor plays a US Navy SEAL in the new war movie and revealed an average day of filming would entail running through burning buildings, dodging gunshots and ducking behind cover from explosions.
The former 'Office' star said: "There was a lot of machismo and a lot of adrenaline on set. A normal day would be running through a burning building. That building you see in the movie? That was actually on fire... I'd say 98 to 99 per cent of this was 'practical', meaning any time there was an explosion, fire or a gunshot, we were walking by those things."
John lost 21 per cent of his body fat for the Michael Bay directed film and although he was working in a fake war zone, he says it didn't stop his body going into the natural "fight-or-flight".
He said: "As an actor, it really helped. There's a primal fight-or-flight instinct that kicks in. Even though it was all pretend, my body didn't know that, so it got freaked out and tried to survive."
The actor - who is married to British star Emily Blunt - comes from a military background and was honoured to play the part of a serviceman.
He told Metro newspaper: "I come from a huge military family with aunts and uncles and cousins who have served or are serving. So I have always wanted to do a movie like this. One that honours what the real guys in this story actually went through."