What would you do if you came face-to-face with a doppelganger?
Canadian director Denis Villeneuve explores that question in the psychological thriller "Enemy," in theaters on Friday, based on Jose Saramago's 2002 novel "The Double."
Jake Gyllenhaal, 33, plays both Adam Bell, a teacher struggling to commit to a relationship, and Anthony St. Claire, a married aspiring actor. The two men are unrelated but look identical.
Adam discovers his double while watching an obscure film and descends into an obsessive search for Anthony. When the two meet, their lives become intertwined.
Gyllenhaal, who had to maneuver special effects and act with tennis balls used to digitally place Adam and Anthony on-screen together, said the film was "the most fulfilling creative experience" for him.
"Never have I had the opportunity to feel what it was like to act against my own instincts, and I actually was humbled by it," he said in an interview littered with laughs, Jay Z quotes and talk of serial killers.
"I think there were places where I thought I knew what I was doing, but then as I'd watch those and do it back, it wasn't easy to work with as I thought it would be."
"Enemy," billed as an erotic thriller, follows Adam as he faces an identity crisis. At times, the audience is taken into his psychological state, which Gyllenhaal described as "his anxiety, his questioning, the feelings that we feel inside of ourselves when we're faced with who we really are and who we perceive ourselves to be."
"The internal journey is the most interesting one to me," he said.
Gyllenhaal gained critical praise last year for his performance as the obsessive Detective Loki in Villeneuve's "Prisoners," a thriller on child abduction co-starring Hugh Jackman. "Prisoners" was made after "Enemy" and reunited Gyllenhaal with the director.
The actor credited "Enemy" for enabling him to push himself to deliver intense scenes as Loki.
"'Enemy' was much more artistically indulgent in the way that we were experimenting with form and process," Gyllenhaal said.
"I was definitely not the center of attention on 'Prisoners,' I was doing my thing along with a number of many more talented actors than I am. Denis said very specifically to me before we started 'Prisoners' ... 'you're not going to get my attention in the way that you did,'" he added.
Gyllenhaal, whose parents are writer-directors and whose older sister Maggie is an actress, forged his acting career in his teens with breakout roles in 2001's cult hit "Donnie Darko" and in 2002's "The Good Girl" as a psychologically unstable young man.
After a leading role in 2004's blockbuster disaster film "The Day After Tomorrow," the actor earned a best supporting-actor Oscar nomination in 2006 for his portrayal of a gay cowboy opposite Heath Ledger in "Brokeback Mountain."
He has since stayed with darker dramas, as with 2007's "Zodiac" and 2009's "Brothers" and more recently, a police officer who becomes entangled in the drug cartel world in 2012's "End of Watch."
The darker characters are getting harder to leave behind at work for the actor.
"You make physical transformations or you make mental transformations; the inside transformations are a lot harder, and they take a lot out of you," Gyllenhaal said.
"I can't just jump from one thing to the next, that's something I've learned. Once I've explored one world, I need some time back in my real life before I can even know what's right for me as an actor to go to next."
After the slew of dramas, the actor will be seen in director David O. Russell's comedy "Nailed," but he will return to grittier roles in "Nightcrawler" and "Everest."
"The exploration of the darker side of things really only allows me to appreciate the other side, you know. So the more I go (to the darkness), the more I can go the other way," Gyllenhaal said.
Then, with a laugh, he added, "But I don't need to go the other way," as if to say that the darkness suits him just fine.