Mendelsohn says he's sure it's the "AC/DC ... Bon Scott kind of effect", and Dominik agrees.
"They really like a masculine male in America, they're in short supply there," he says.
"And they don't mind if he's got a drug problem."
Which there's no doubt Mendelsohn's character Russell has. Full of get-rich-quick schemes, he wants only to make a lot of money so he can become a dealer and get his fix for free.
That leads Russell to team up with Frankie (Scoot McNairy) in a hare-brained scheme to knock over a mob-run card game, supervised by Markie Trattman (Ray Liotta).
Mendelsohn says although growing up in Australian cities exposed him to many junkies, which helped him in the role, there's a lot more to Russell than the monkey on his back.
"What Andrew ... told me was he is basically a filthy, pleasure-seeking, dog-loving hedonist, and he looked at me and said 'can you handle that?' and of course, it's a pleasure," he says, grinning.
One of Russell's schemes involves dog-napping purebreds and driving them to Florida for re-sale, which leads to a couple of laugh-out-loud moments in a movie that otherwise seems painted in shades of bleak.
But it's when the heist happens that Mendelsohn's acting really shines, as he has to carry out the robbery in a mask and without speaking, to hide his Aussie accent.
"That whole sequence was an awfully tough day or two ... in this weird little clam restaurant," he says.
But he says it really reflected Dominik's film-making ethos to let the surroundings set the mood.
"It's a lot of fun when it's like that, even when it's awful it's a lot of fun and as actors, you're really just eating that stuff up."
While Killing Them Softly may be billed as a Brad Pitt film, audiences may be surprised by how long it takes for the Hollywood star to make an appearance, although he doesn't disappoint when he does.
Set in 2008, the film shows New Orleans still recovering, almost three years after Hurricane Katrina, with the United States slipping into the despair caused by the global financial crisis.
Dominik says he used audio and video from news items of the day to illustrate the levels of criminality in US society.
"America's kind of rotten all the way through, is kind of how it seemed to me," he says.
"Crime and capitalism are kind of the same thing really and the rules of what's allowed and not allowed gets more complex the more civilised society gets."
Who: Actor Ben Mendelsohn and director Andrew Dominik
What: Killing Them Softy also starring Brad Pitt, Ray Liotta
When: Opens in cinemas on Thursday
- TimeOut / AAP
