For Tim Burton, his movie "Frankenweenie" is a labor of love -- right down to the stars he cast to voice the animated characters in it. Both Martin Short ("Mars Attacks") and Catherine O'Hara ("Beetlejuice") have worked with the director before, and were happy to work with him again -- even if that didn't leave a ton of time for prep work. "It's not even a meet, you go right to the studio," O'Hara says. "They'e got the drawings up on easels and walk your through the characters and tell you about the story."

Not that the two stars, who provided a multitude of voices, were expected to create them on the spot. "It's a process," says Short. "No one's expecting you to go do Weird Girl, jump off the diving board of it. Maybe it's good to take two sessions to find what the voice should be…Usually by the end of the first session when you start the second, Tim will go, 'I've been listening to the tapes and I really like it when you're in the lower register and that creepier guy,' and then he plays it back, oh okay, then you're almost there… but it's a process."

Both O'Hara and Short, who may be best known for their sketch and improv work ("Best in Show," "Saturday Night Live"), were given free reign to improvise, though they knew what isn't in the script may not make the final cut. "You've got a great script, great lines, and these great drawings that are inspiring," says O'Hara. "[Burton] knows these characters, but is definitely open to any ideas we might have to voice them.

"You're there and might improvise for 20 minutes and you're convinced you're really improving the script, but if he doesn't like it?" Short says. "He's the painter and we're just giving him different colors of paint."

Considering most of their colors are pretty funny, they also joked around during our interview. When Short brought up the issue of payment, he deadpanned, "We have the same manager, strangely enough, so I said what is Catherine getting paid -- and double it."