Until he nails it—not with horror but with old-fashioned anxiety. Villeneuve and Gyllenhaal quickly agree it's the best expression. The decision is key, since it will be the take that Gyllenhaal, as Anthony, will be acting against when his two opposing selves meet.

After readying himself to inhabit the part of the vain actor, Gyllenhaal heads off to shoot publicity stills in a nearby room. Flashes go off, and then an imposingly handsome man in a leather jacket and motorcycle boots barrels out with that broad-shouldered, get-the-fuck-out-of-my-way gait such men move with. It takes a second to register it's Gyllenhaal, as Anthony.

Back on-set it is hard to say what's so different about him. Something—everything—seems changed. "Beard's the same," Villeneuve says. "The only difference is that Anthony's hair is higher, and Jake pats it down so it's not so obvious. It's all him—the 'special effect' here is Jake."

"I'm fucking crazy?" says Gyllenhaal as Anthony, walking threateningly toward "Adam," a chest-high foam pad, which he'll grab, jab, or bitch-poke in the chest. "I'm fucking crazy?!" This is still rehearsal, but Gyllenhaal's menace as Anthony is already being calibrated.

A production assistant tells me my ride to the airport is waiting. As I gather my things, a scream comes—"I'm fucking CRAZY?!!"—followed by a thwack of the pad so hard it literally shakes the set, on which quiet suddenly reigns.

As I leave, I see Villeneuve talking to someone at the top of a gangway. Both men slump against the wall, immersed in thought. I start to thank Villeneuve for his hospitality, when the man next to him wishes me a safe flight. Of course, it's Gyllenhaal. He's still in Anthony's clothes, but, deep in reflection, he no longer has that actorly swagger or the violence that was just on display. As I bid him good-bye, I have the strangest feeling I don't have a clue who I'm saying it to.

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