"It really stuck with us when we read the script," Carell said about the dark comedy. "It was very different than anything I'd ever read."
Knightley agreed, saying the story takes a unique approach.
"I've never read anything like it. Particularly taking this subject matter, but making it this kind of dark comedic, kind of strange thing as opposed to this big action adventure, I just thought it was such a unique way of telling this kind of a story," said Knightly.
In this movie, Carell's real-life wife, Nancy, makes an appearance.
"The director called and asked whether Nancy would play my wife in the movie, a very pivotal scene at the very beginning," Carell said. "She just said, 'Of course. It just sounded like fun - sounds like fun to leave you, ha ha.'"
She's out, but a little dog is in for the adventure. The dog that appears in the film is a rescue.
The film opens Friday and is rated R.