Writer/director John Michael McDonagh admits he hesitated before casting Domhnall Gleeson in the small but pivotal role of serial killer Freddie Joyce in his latest film, the blackly humorous drama Calvary. For Gleeson—whose credits include both parts of Harry Potter and the Deathly Hallows, True Grit, Anna Karenina, the upcoming comedy Frank, and a Tony-nominated turn in Martin McDonagh’s The Lieutenant of Inishmore—it would be casting again type, but that wasn’t what concerned McDonagh. It was just that in this single scene, Domhnall would be acting against Calvary‘s star, Domhnall’s dad, Brendan, playing a priest whose week starts with a death threat and doesn’t get any better with his jailhouse visit with Joyce.

“I was a bit worried about it, because I thought it would bring the audience out of it. They’re going, ‘Oh, that’s Brendan Gleeson. That’s his son,” McDonagh says.

“It’s a very intense scene obviously,” he adds. “There were a lot of things being said that unnerved people in the crew as they were listening to it. And we go from a very big wide into really close. It’s very intense … It’s deliberately a kind of black hole right in the middle of the film. I think it’s about 50 minutes, so it’s right dead center.”

For Brendan Gleeson, sharing the scene with his eldest child was a revelation. They have acted together before on a number of occasions, including a 2006 Irish football comedy Studs and Ian Fitzgibbon’s 2009 comic thriller Perrier’s Bounty, and Domhnall directed his old man in his 2010 short Noreen.

But Calvary is different. Brendan Gleeson remembers reading through the scene with Domhnall in rehearsal, and then the younger Gleeson went away until it was time to shoot it, adopting radio silence with his dad as he worked to find the character. On the day, Domhnall was not only in character, but McDonagh had directed hair and makeup to make him as unrecognizable as possible.

“It was very difficult in a sense. It was a harrowing day,” says Brendan Gleeson.

“We had kind of retreated to our separate corners and we just came out fighting on the day. Then we sat down at this table in this vast room and we didn’t really talk to each other very much. My analogy for it afterward was we were two sparring partners who were great friends or brothers or something, but when you do it in the ring for real, you have to park all that stuff and just fight your corner, basically, and that’s what we did.”

The scene between Freddie and Father Michael is an arresting one, one of the darkest in the movie, and one that McDonagh discovered, from Calvary‘s first screenings at the Sundance Film Festival where the movie premiered, has a curious effect on audiences.

“After that scene, I thought, ‘That’s going to turn the film into a really dark, somber place,” says McDonagh. “What I found … was that we would still get laughs after that sequence and they would be bigger laughs than what I was expecting. I think it’s because that scene is so dark and somber that the audience wanted relief from it. They’re looking for any kind of relief and so they laugh a bit more than probably they should.”

For Brendan Gleeson, it was just a relief to finish the scene.

“It was fantastic to work with Domhnall, but in retrospect, it was nice to get him back at the end of the day,” he says.

Gleeson starts to say that in that scene he saw in his son something that he’d never seen before, but then he corrects himself. That face, the expression on Freddie Joyce’s face, that was familiar.

“When I tried to get him out of bed too early maybe over the years, I’ve seen that look before,” Gleeson laughs.

“I think Domhnall did extraordinarily well,” he adds more seriously. “He’s quite chilling. I’d be proud of him, anyway, but I was particularly so after that.”—Pam Grady

For more of my Brendan Gleeson interview, click here.