One of the great surprises of the fall isn't just how funny the Woody Harrelson comedy "Zombieland" is, but the unexpected left turn the apocalyptic road trip flick takes about halfway through.  At this point, almost everyone knows the twist is the appearance of  Bill Murray playing himself in a zombie-decimated world. Up until now, however, we haven't heard why he agreed to mock both himself and his signature role in "Ghostbusters" (a franchise with a third installment in the works) in the smash horror comedy.

Speaking in the English countryside while promoting the new Wes Anderson stop-motion animated "The Fantastic Mr. Fox" today, HitFix asked Murray how he came to find himself playing himself alongside old buddy Harrelson. 

"Well, I haven't seen it either so I don't know what you are even talking about, because I'm not even in it," Murray says with a smile.  "If I were in it, I would say they wanted Joe Pesci for the part and Woody called me up.  And I know Woody, we did 'Kingpin' together and he's a great guy. And he said, 'Pal, would you ever like to play a Zombie?' Here's the deal.'   And he goes, 'And we go to a house and it's your house.'  And I'm like, 'What? Did you just wake me up?"

Murray continues, "I just thought playing yourself as a zombie was irresistible. And I thought Pesci was a fool.   Pesci would be a spectacular zombie.  Just imagine that guy with super-human zombie powers. He's already like that. In a way I thought, 'He missed the boat on this one.'  Even while we were shooting, 'Why did he not do this? This is crazy.'"

It turns out Pesci wasn't the only actor considered for the role.  Sources tell HitFix that at one point Matthew McConaughey was supposed to play Tallahassee's cinematic idol, but he became unavailable at the last minute.  That appears to be when Pesci and Murray came into play.

As for his "Zombieland" co-stars, working with Harrelson again was "really wonderful" according to Murray, but it was Emma Stone that impressed him the most.  His eyes lit up when praising the "Superbad" comedienne.

"I really like that girl Emma.  She's funny. She's really, really got it," Murray says. "I had to be out [cold in a shot] and they had to be talking over me.  They did 15 or 20 takes and she made me laugh every single time. I had everything I could do to stay dead.  It was really funny."

Look for more from Murray and his "Fantastic Mr. Fox" co-stars George Clooney, Bill Murray and Jason Swartzman tomorrow and Thursday on HitFix.