As Tom and Violet in The Five-Year Engagement, the pair find a myriad of obstacles prevent them from walking down the aisle.
Digital Spy sat down with the duo to talk about doughnuts (which play a key part in the film), Emily's bang-on impersonation of the Cookie Monster, and why Jason wants to star in The Devil Wears Nada.
"I learned that Emily Blunt is fantastic at comedy. I knew she was funny in real life but I didn't know she was going to come and dominate the screen," Segel said of reuniting with his Gulliver's Travels co-star.
Blunt added: "I'll say the opposite - I knew you were funny but I learned how moving you were in the sad moments, in the hospital scene with your amputated toe, that was so sad."
Of her impersonation of the Sesame Street character, Blunt said: "They called me and said, 'Hey, we're going to do a table read'. They're quite clever this crowd because they do a table read in front of an audience of 60 people to see what's funny.
"I was quite nervous about it. They sent me the script and there's a new scene where I have to speak in a Cookie Monster voice. I knew his voice, but I went online and studied."
The Five-Year Engagement opens in UK cinemas tomorrow (June 22).