I’ve seen Batman v Superman: Dawn of Justice three times now, and at every screening there were big laughs when Batman yells out “oh shit!” when he comes face-to-face with Doomsday. It turns out, that wasn’t in the script, and was something that Ben Affleck improvised on set. He explained the decision in a new interview with Entertainment Weekly.

“I just improv’d that. I had a feeling that it would work and that it would be funny,” the actor says. “I improvised and I talked to Zack about it and I think this will really work because you don’t expect it – and because it’s Batman, and at that moment he is so incredibly overmatched.”

Affleck thought the line actually humanized the character. “We’ve taken these characters and are treating them more and more realistically,” he says. “It seems very realistic that he would say that at that point.”