The two star in the upcoming film, which centres on a couple whose engagement keeps getting postponed. Blunt revealed that Segel was required to fake an orgasm for one scene.
"We have a really bad [sex scene] with a fake orgasm happening on Jason's part, which is even funnier," she told Collider.
"You guys were like, 'Yeah. That happens a lot with girls', but this is actually from a guy," Blunt continued, turning to Segel.
The Muppets star added that he went through a number of takes for the scene in question.
"I did quite a few takes, but I can't give away my secrets or the context in which it happens," he said. "So you will just have to watch."
The Five-Year Engagement will open this year's Tribeca Film Festival, which takes place in New York from April 18 to April 29.
Segel's Twitter account has recently fallen victim to a number of hackings. The actor expressed his confusion over being a repeat target.
"Twitter account hacked again. I don't understand the point of what you're trying to do hackers. Why? Sorry to anyone following me," Segel wrote.
Watch the trailer for The Five-Year Engagement below: