Ben Affleck had to master an Indonesian martial art for his new film The Accountant.
Director Gavin O'Connor introduced the actor to full-body fighting form Pencak Silat, and told him he would have to train to perfect it, because there wouldn't be many opportunities to call in a stuntman.
"It's an Indonesian style of fighting which was very cinematic, kind of flashy but very efficient which matched the character," Gavin told WENN. "When we honed in on that, our guys just started training Ben."
And the Argo star admits training in the physical defence practice was tough going.
"Gavin was concerned that the action be real and good, something he's done really well in (previous film) Warrior," Ben explained. "So training was as much a part of this as it was for Batman.
"It's a lot harder in this one for the stuntman to do your stunts when you're not wearing a mask! I had to really be on top of my game and work out with professionals who educated me about this fighting style."
Ben plays Christian Wolff, a mathematics genius whose emotionally stilted personality results in him having a difficult relationship with his son, in The Accountant.
And the 44-year-old star previously revealed that the film's complex take on parenting is what drew him to the role.
"Here's a guy out of love and compassion and fear for his son, actually ends up kind of brutalising him and abusing him and it's a really interesting look at what's the appropriate way to channel the intense emotions we have as parents, it's not easy," he told America's People magazine.
Ben is father to 10-year-old Violet, seven-year-old Seraphina and four-year-old Samuel with estranged wife Jennifer Garner.
The Accountant, which also stars Anna Kendrick and J.K. Simmons, opens in theatres on 14 October (16).