You make adjustments according to the specifics of the character.It's something I feel like a lot of my comedic heroes have always done. It's not even necessarily vulnerability, always, but it's an earnestness, a genuine desire to actually do the right thing, but then still make really misguided, stupid decisions along the way.

One of the biggest breaks we had actually, one of the biggest, the hardest I laughed on the movie [The Hangover] was the baby was just doing ridiculous things and making hilarious faces. But I'm sitting there and I'm supposed to be having this exchange with Zach [ Galifianakis] and the baby is like staring at me with these huge eyes and acting, and just making the most cerebral faces, and I could not keep it together.

I was just fooling around with the piano and Todd [Phillips] was like, 'Hey there's a great spot in the movie [The Hangover] where we need a little bit of a breath in the narrative. You should write a song and stick it in there.' And I was like, 'Well, what should the song be about?' And he said, 'The tiger.' 'Oh, okay.' So I went off and I wrote this song. I came back and Todd and I tinkered with it a little more and then we shot it right then. It all happened in a day.

I'm sort of laughing and so Zach [ Galifianakis] started laughing [on the set of The Hangover]. And Todd [Phillips] was baffled because what we were saying wasn't that funny, you know what I mean? And it was like all the baby's face. So Todd was like, 'What is going on? Get it together guys.'

People now genuinely respond to it and associate me with music. It's really fun.

We played around and improvised a ton [in The Hangover], and I think it's hard to say at this point what's what. Gosh, I wouldn't even know how to take a stab at it. The script was so good that we really didn't need to improvise very much, but I think we just found a lot of moments on the set. It's really cool when you get onto the set of a movie and you start shooting the scenes and you start to actually incorporate the environment.

What's cool is that in the story of the movie [The Hangover] our characters are also really kind of getting to know each other and bonding over the course of the movie. And I think you're seeing a real, a literal sort of friendship growing both in us as actors and on screen as characters.