LOS ANGELES—There are certain Hollywood rules that are usually strictly enforced. One of them is that animated voice-overs are done separately, particularly when big stars are involved. That allows the actors to mosey into a local studio when they’re shooting on location and do the work at their leisure. However, Tom McGrath, the director of Megamind (which opens Friday [November 5]), thought it would be more interesting to have Saturday Night Live alumni Will Ferrell and Tina Fey work out scenes together and make changes to the script if they thought they were warranted.

“We wanted them to be able to be partners and collaborate,” he says in an L.A. interview room. “I would say that 30 percent of the things that you see and hear are improvised in some way because not only are they great actors but they are great writers as well. So we come in with our [scripted] lines, and on a scene-by-scene basis, we get three alternative lines for every written line.”

The movie stars Ferrell as Megamind, an alien being with superpowers who learns early on that he is well suited to villainy. His nemesis is a superhero named Metro Man (Brad Pitt), who continually saves the day and rescues feisty reporter Roxanne Ritchi (Fey) from Megamind’s clutches. When things don’t work out as planned, Megamind assumes he will have to go out and find a new enemy. He needs someone who can help him out, and he looks to an unlikely source for assistance.

Fey jokes that she came to the role from the perfect place. “I am one of American’s foremost fake reporters, and I am going to have a fake show on CNN,” she says. “It was fun to step into this archetypal Lois Lane character. I liked the fact that this is a modern version of that and that she is active and intelligent. I really liked how she looks, with her short brunette hair and her ample can. I liked how she was drawn.

“I thought the recording sessions were very freeing,” Fey continues. “If you are filming something and you are improvising, you feel you might be wasting film and the cameraman’s time, but when you are recording stuff first, you are trying a bunch of things and it doesn’t matter how you look while you are doing it. There is a complete absence of vanity.”

On November 9, Fey will become just the third woman to receive the Mark Twain Prize for American Humor. (Whoopi Goldberg and Lily Tomlin have also won it.) She says she isn’t sure why she’s being given the award but that she’ll be thrilled to accept it. “I can’t understand why that is happening. I mean, I am honestly very honoured, almost to the point of being embarrassed, and I am looking forward to receiving the award. Mark Twain was a great American humorist who is taught in schools, which is a big deal, and I hope that one day Hal Holbrook [a Mark Twain impressionist] has a one-man show about me.”

Although she’s been at the forefront of TV comedy, thanks to her dual roles as writer and star on both Saturday Night Live and 30 Rock, it’s possible that Fey is getting the award, which goes to comedians who’ve had an impact on American society, for doing one of the more acclaimed impressions in recent American history. She admits that having the chance to play former U.S. vice-presidential candidate Sarah Palin on several episodes of SNL was a big break and maybe even a bit of a fluke.

“That [doing impressions of Palin] was one of the luckiest things that ever happened to me, and I am going to milk that ride,” she says. “I am going to be doing it, God willing, when I am 70. I will be doing that at auto shows if things go right.”