Jason Segel stars in "The Muppets." Jim Spellman/WireImage.com
We're almost the same age, which would have made you just 1 when "The Muppets" show ended its run. How did you come to love it?
"Yeah, we were the tiniest bit too young to have caught it, but my mom taped all the episodes and made sure that she showed them to me. She was kind of a student of comedy herself."
Were you also a fan of the old Muppets movies?
"Yeah, the first three ['The Muppet Movie' (1979), 'The Great Muppet Caper' (1981), and 'The Muppets Take Manhattan' (1984)] are the pantheon that we really tried to copy in tone to get where we are with this movie."
So why not just let those movies be their legacy? Why make another?
"I think that it's important for kids to have the same experience we had with the Muppets. I think it would be selfish to just leave them for our generation. They're such a force for good, and they teach such nice lessons about teamwork and the idea of being better together than you are apart. And they never get laughs at other people's expense."
Jason Segel is all smiles with the Muppets. Walt Disney Pictures
There were jokes both kids and adults would enjoy. Did you write certain jokes for each age group?
"[No] I think that that's kind of the magic of the Muppets -- they're not just kids' entertainment. They truly are family entertainment. The Muppets have always felt a little bit dangerous. And they're like this controlled chaos that's on the verge of bubbling over. And so I think what's fun is a whole family can really go and enjoy it together."
A lot of movies about nostalgic subjects are parodies. Did you ever think of making it a parody?
"No, there was no part of us that ever considered doing the Muppets with a sense of irony. I think that would have been disrespectful to the legacy."
Your character Gary's performance of the ballad "Man or Muppet" is hilarious. How involved were you in creating that?
"That song was written by Bret McKenzie from [former HBO musical comedy] 'Flight of the Conchords.' He was our music supervisor. And I really feel like that song should be nominated for an Academy Award. I think Bret McKenzie just nailed it, and he was the perfect man for the job. 'Flight of the Conchords' is very Muppet-y: Two wide-eyed innocents kind of trying to make their way through the scary world, and they never make fun of anyone either. So they reminded me of the Muppets very much. "
Jason poses with co-star Amy Adams. Todd Williamson/WireImage.com
Some of the musical numbers were large and seemed to involve the entire cast. How did the rehearsals go?
"It was great. I've always loved the MGM-style lavish musical numbers, like 'Singing in the Rain' is one of my favorite movies. And it's also part of the Muppet tradition, big song and dance numbers. So I was really excited to be a part of it. We had a great choreographer named Michael Rooney, who is actually Mickey Rooney's son. And he did a great job. [Amy Adams and I] learned the final dance number the night that we did it. They choreographed for weeks and weeks and weeks, but because of our varying schedules, a lot of the dancing was learned on the spot. But the opening number, that was about a week of rehearsals."
You've also danced on "How I Met Your Mother." Are you confident in your dancing ability?
"This body was made to dance."
Did working with the Muppets take away from the fantasy you had of them at all?
"No, I'd been working with puppets for a long time, and I had that lavish puppet musical at the end of 'Forgetting Sarah Marshall,' so I was pretty familiar with how it worked."
Because usually ...
"Yeah, you don't want to see the man behind the curtain."
Exactly! So it didn't ruin anything for you?
"No, not at all. If anything, I walked away with a greater admiration for those puppeteers."
Jason and Alyson Hannigan star in "How I Met Your Mother." CBS
I also wanted to ask you about "How I Met Your Mother." Alyson Hannigan's character, Lily, and your character, Marshall, are expecting a baby soon. How do you think that will change the show?
"Well, what's good for me and Alyson Hannigan is that you can only work a baby so long, 'cause it's a baby, and it doesn't know that it's acting. So hopefully our hours will be shorter."
How much longer do you plan to stay with the show?
"We're all signed through season eight, so that'll be [the rest of] this season and the next season, and then we'll see what happens from there."
You recently lost 30 pounds. How did you do it?
"The studio for the next movie I did got me a personal trainer, because they said it had to be at all conceivable that Emily Blunt would ever date me. [She's his co-star in the April 2012 comedy 'The Five-Year Engagement.'] So they hired a personal trainer, and I just worked out every day. I limited my drinking and tried to watch what I ate."
Would you be open to doing another Muppet movie?
"Well, I'm very superstitious, so I'm just trying to wait to see how this one does, but my goal was to create a platform for the Muppets to kind of do anything they wanted from this point on."
But would you like to be involved in that?
"I always say I serve at the pleasure of Kermit the Frog."
- Forgetting Sarah Marshall