Bill Murray doesn't do interviews unless he feels like it, which hasn't been often in the past decade. As Dan Fierman puts it in GQ:
The very thing that makes Bill Murray, well, Bill Murray is what makes sitting down with him such an unpredictable enterprise. Bill Murray crashes parties, ditches promotional appearances, clashes with his friends, his collaborators, and his enemies. If you—movie director, journalist, dentist—want to speak to him, you don't go through any gatekeeper. You leave a message on an 800 number. If Bill Murray wants to speak with you, he'll call you back. If his three and a half decades in the public sphere have taught us anything about the 59-year-old actor, it's that he simply does not give a good goddamn.
You have a lot of lines in this one that get tons of laughs I doubt were on the page. It's all in the rhythm, the delivery. How do you pitch something like that? How do you make something out of nothing?
I have developed a kind of different style over the years. I hate trying to re-create a tone or a pitch. Saying, "I want to make it sound like I made it sound the last time"? That's insane, because the last time doesn't exist. It's only this time. And everything is going to be different this time. There's only now. And I don't think a director, as often as not, knows what is going to play funny anyway. As often as not, the right one is the one that they're surprised by, so I don't think that they have the right tone in their head. And I think that good actors always—or if you're being good, anyway—you're making it better than the script. That's your fucking job. It's like, Okay, the script says this? Well, watch this. Let's just roar a little bit. Let's see how high we can go.
But you asked how you get the comic pitch. Well, obviously a lot of it is rhythm. And as often as not, it's the surprising rhythm. In life and in movies, you can usually guess what someone is going to say—you can actually hear it—before they say it. But if you undercut that just a little, it can make you fall off your chair. It's small and simple like that. You're always trying to get your distractions out of the way and be as calm as you can be [breathes in and out slowly], and emotion will just drive the machine. It will go through the machine without being interrupted, and it comes out in a rhythm that's naturally funny. And that funny rhythm is either humorous or touching. It can be either one. But it's always a surprise. I really don't know what's going to come out of my mouth.