Chief among them was Robert Pattinson, who admits to being in the "very obvious throes of a panic attack" before production began in Toronto in May 2011.
At a Toronto press conference on Monday, the "Twilight" heart-throb said he and co-star Jay Baruchel were "absolutely terrified" when shooting the first scene of the film that's based on the 2003 Don DeLillo novel of the same name.
Director David Cronenberg's calm demeanour put him at ease, as did a pre-shoot chat at the filmmaker's house in which he told him to "stop worrying."
*More under the cut*
"I think you were just placating me by saying to come around," Pattinson told Cronenberg with a laugh at the media event attended by the director and several of the film's stars.
"But I think you just said, when we started shooting, 'What will be will be.'"
Pattinson is earning raves for his performance in the film, which recently debuted at the Cannes Film Festival and opens across Canada on Friday.
He plays Eric Packer, a stony 28-year-old Manhattan billionaire asset manager who goes on a fantastical road odyssey in his white stretch limo to get a haircut at the other end of the city. Along the way he runs into a mess of traffic caused by a visit from the U.S. president as well as anti-globalization protests.
As Eric meets with various associates both inside and outside the limo, he encounters some sexy, gory and life-threatening scenarios — all while ruminating on his lost fortunes and his mortality.
Other co-stars include Juliette Binoche, Sarah Gadon, Kevin Durand, Samantha Morton, Paul Giamatti, and Emily Hampshire.
Cronenberg said he changed a few scenes from the book for cinematic purposes, but kept most of the literary dialogue the same, feeling it was "very stylized," "Pinteresque" and yet "realistic."
And he told his actors to stick to the lines, adopting a mantra that's mentioned in the film: "Let it express itself."
Pattinson said he had trust in Cronenberg and was relieved he didn't have to come up with his own interpretation of his complex character.
"I mean, I'm not a post-modernist, like, scholar or anything," mused the British superstar, looking relaxed in a black sporting jacket and black golf shirt.
"Your agent said you were," quipped Cronenberg, eliciting laughter from the roomful of journalists who were warned by the panel moderator not to ask "vampire, werewolf or personal questions."
"So I'm sitting there thinking, 'Can I come up with an interpretation of DeLillo that's completely original in two weeks?' added Pattinson, 26. "I mean, that's completely ridiculous.
"But there's something about the construction in his writing that's so easy, you don't need to add anything to it, and I think that's just what (Cronenberg) encouraged me to do."
Giamatti, whose troubled character is obsessed with Eric, filmed "Cosmopolis" at the same time he shot the upcoming musical film "Rock of Ages."
"I was panicked about it," said the Oscar-nominated actor of "Cosmopolis." "This thing was intimidating. The length of it and the language and stuff, and so I was bothering everybody I could on this other movie, to read this thing with me."
"Fortunately ('Rock of Ages' co-star) Malin Akerman made a great Rob Pattinson for me. She was fantastic. It was very disappointing when I actually got here and it was Rob," a bearded Giamatti added jokingly.
"But God bless, that woman sat and read that thing with me over and over and over again, because I just needed to feel that security."
Most filming for "Cosmopolis" took place undercover at an east-end studio in Toronto. But the public shoots drew in some paparazzi and fans, many of them Pattinson admirers.
"Whenever we were on a location, it was incredible, it was a phenomenon," Durand, who plays Eric's chief of security, said in a recent interview.
"I've never seen camera lenses like this, lenses that were like the size of a Lincoln Town Car shooting from, like, a mile away. And (Pattinson) would point them out to me and I'd be like, 'Oh my God, that's so nuts.'"
Durand noted that while shooting the film, his wife called him and told him she saw a paparazzo's shot of him in the apartment in which he was staying.
"Someone was shooting me on a long lens in my apartment, and that's all a byproduct of being in a Robert Pattinson film, I'm sure," said Durand.
"(The paparazzi) were all over the place. It was incredible, and you know, he really greets it and acquiesces to it in a really great way. He's quite gracious. I was really impressed with him, and I think he's a really good actor. He's great in the movie."
Pattinson said he didn't notice a "massive difference" between the amount of fans gathered around the set of this film compared to his other projects, which also include "Water for Elephants" and "Harry Potter and the Goblet of Fire."
"Generally people are pretty nice," he noted. "It's very confusing as to why people will sit there and watch for a long time.
"But this film was a little bit more frightening. The first scene, which we did, I think it was the first time I was outside of the limo and there was a big crowd lined up."
Cronenberg said dealing with onlookers at his film shoots also isn't foreign to him, noting he's also made movies with handsome stars including Jeremy Irons and Jude Law.
But he conceded the recent "Cosmopolis" premiere in Portugal drew in an "unusual" frenzy.
"There was a red carpet that was about a mile long and it was lined with literally a thousand screaming girls, and they weren't all Portuguese either. Some of them were saying, 'Come to Russia, come to Russia!' So I knew they weren't Portguese.
"That was kind of like the Beatles and I had not experienced anything like that before."