It's not the same thing, playing a bug-eyed bad guy in a live-action chase around Manhattan, as Michael Shannon did in last summer's Joseph Gordon-Levitt bike messenger romp, Premium Rush, and playing a real-life mob contract killer.
A killer with more than 100 victims on his resumé.
And a killer who could go home at the end of the day after shooting, stabbing, or poisoning his prey and settle in for a cozy night with the missus and kids.
Which is what Richard Kuklinski, the man Shannon makes disturbingly real in The Iceman, did. A hit man active in New Jersey and New York for decades, Kuklinski won his nickname for hiding bodies in the freezer. Ultimately he was caught, tried, and sentenced to life in prison. He died in 2006.
For Shannon, nominated for an Academy Award for his portrait of a palpably unsettled but prescient mental patient in 2008's Revolutionary Road, getting into the mindset of a professional killer was a challenge.
"Anthony Bruno, who wrote the book The Iceman and who interviewed Kuklinski in jail, told me that he was like an animal," Shannon says. (Bruno, the true-crime and fiction writer, lives in Philly.) "Animal-like in his alertness. You feel like he's breathing you in. He's figuring you out every second he's around you."
Shannon conveys that heightened sense of awareness - and tension - in the film, which opened Friday at the Ritz East. Winona Ryder plays Kuklinski's seemingly clueless wife, Ray Liotta is a local crime boss who gives Kuklinski his first job, and Chris Evans is a fellow freelancer. To understand the character and what he did, Shannon says he tried to visualize what was going on in Kuklinski's head.
"This may sound like Pop Psychology 101, but it made sense to me: That every time he was sitting across from a guy, about to blow his brains out, he was basically going through his relationship with his father," Shannon says. Kuklinski's childhood was traumatic; he and his brother were physically and psychologically abused by their dad.
"It was all about dominating that person that had threatened him so much when he couldn't protect himself," Shannon explains. "It's like he was saying, 'Now that I have the ability to assert my dominance over you, I'm going to do it.' And so the murder is the act of dominating the father.
"The problem is that it never really works. Because you can never really get revenge - that's the one thing that human beings never seem to understand."
Shannon, who stars as the bootlegging enforcer Nelson Van Alden in HBO's Boardwalk Empire (he was shooting a fourth-season episode into the wee hours the morning before this phone interview), has been working nonstop over the last few years. Next month, he will be seen playing General Zod - the mad Kryptonian who comes to Earth to nemesize Superman - in Zack Snyder's Man of Steel.
"This is the way it went down," reports Shannon, rattling off the order of his projects. "Right before Iceman, I finished Man of Steel. And right before Man of Steel, I finished the second season of Boardwalk. And then after Iceman, the third season of Boardwalk. And then -."
And then he did Grace, a Craig Wright play, on Broadway. And then he did The Harvest, a psychological thriller with Samantha Morton. And then he did Young Ones, a futuristic eco-thriller with Elle Fanning and Nicholas Hoult. Shannon is talking with Jeff Nichols, for whom he starred in 2011's haunting Take Shelter, about a new project for the fall. (Shannon has been in all three of Nichols' films: Shotgun Stories, Take Shelter, and Mud, currently in theaters.)
There's also "Michael Shannon Reads the Insane Delta Gamma Sorority Letter," a must-see Funny or Die Web video, in which a volatile Shannon reads a hysterical admonishment of an e-mail from a concerned sorority sister.
Shannon, who lives in Brooklyn and has a knack for capturing spiritual unease, is, as the Funny or Die video demonstrates, also capable of eliciting laughs. He says something about James Franco - who cameos as a sleazy East Village photographer in The Iceman - that is riotous, but, alas, is also a spoiler.
But he does have kind things to say about two of his other Iceman castmates, Ryder and Liotta.
"The first time I met Winona, I was scared," he confesses. "She's as much a star to me as anybody out there. But she's so down to earth. She showed up, she had a rock-and-roll punk T-shirt on, black jeans, sneakers - she was like somebody you'd meet at the club. She was very approachable.
"And she really nailed the role of Deborah [Kuklinski], I think. She captured the fragility of the woman."
As for Liotta, whose resumé is thick with tough guys and creeps (Goodfellas, The Place Beyond the Pines), Shannon was struck by his explosiveness.
"I remember when I saw him in Something Wild," he says. "I thought he was literally the scariest human being on earth. I couldn't imagine a more terrifying individual."
And was he that way in person, on set?
"He's interesting, because he likes to throw a couple of curveballs at you. He'll screw around a little, just to see if he can get a rise out of you.
"And that was obviously the dynamic in the relationship in The Iceman - [Liotta's] Roy De Meo can't believe he's meeting somebody who might be even more screwed up than he is."