LOS ANGELES -- Animation offers a world of different challenges for actors. Tools like body movement, facial expressions and hand gestures are no longer available to sell a scene.
At the same time, animation offers a world of opportunities: It is the film genre where animals can talk, toys come to life and even a petite Oscar-winning actress can become an all-powerful defender of the galaxy.
It's pretty obvious Reese Witherspoon is never going to get cast as a muscle-bound female crime fighter in a live movie -- at just over 5 feet tall, she's about the size of most action heroes' biceps.
That's no problem in animated worlds.
In the new movie "Monsters vs. Aliens," Witherspoon's one of the toughest action heroes to come along.
"I've been offered a lot of animated films. Sometimes, they were playing the girlfriend and sometimes the girl who got rescued by a guy. I just felt like this was the first opportunity that was presented to me where the woman was at the center of the movie," Witherspoon says during an interview at the Four Seasons Hotel last week.
"That's kind of a unique opportunity for me to create a character that had strength, had a journey, had a whole story line."
Along with Witherspoon, the film features the voice talents of Seth Rogen, Kiefer Sutherland, Will Arnett, Hugh Laurie and Rainn Wilson.
Witherspoon's character is your typical bride-to-be until a close encounter with a meteor turns her into a super-strong giant.
Arnett voices The Missing Link, and Laurie's the voice of half man/half cockroach Dr. Cockroach Ph.D. They become a team that must fight an alien invasion.
"This is the first movie I have ever done that had this much action in it. I was thrilled, because I can't imagine any other world where that opportunity would present itself to me," Witherspoon says.
Witherspoon says that there were recording sessions where she had to run in place, sound winded, make grunting and action-hero kinds of noises that proved physically taxing.
Director Conrad Vernon stresses Witherspoon was a trouper through the numerous recording sessions held over a two-year period.
The most difficult part of directing Witherspoon was trying to get her to sound a little bit more like a superhero.
"They wanted me at the end of the movie to kind of talk with an action-star voice. That is not a voice I know or have in my repertoire. So they kept trying to coach me to be more like Arnold Schwarzenegger or Sylvester Stallone," Witherspoon says.
She deepens her voice and says, "I am Ginormica!"
"They were like, 'No, that sounds like a robot,' " Witherspoon says.
She tries again, "I am Ginormica!"
The actress explains that after several such failed attempts during the recording session for the movie, the director actually told her to stop and drink some tea. Her voice sounded bad.
This is Witherspoon's first animated film. Her co-stars are veterans. Rogen has lent his voice to everything from "Family Guy" to "Horton Hears a Who!"
"I'm sure you've heard the expression that acting is reacting," Rogen says. "Well, if you remove other actors from that equation, then the art of reacting becomes quite different.
"You kind of go in there and you play around and you have a lot of time to experiment and it's just a lot of fun."
Sutherland has lent his voice to "The Simpsons" and "The Wild," while Arnett's voice credits include "Ratatouille," "King of the Hill," "Ice Age: The Meltdown" and the upcoming Fox animated show "Sit Down, Shut Up."
Arnett has done enough work in animated projects that he's gotten comfortable with the limitations of the process.
"Obviously it takes away your physicality," Arnett says. "It is a challenge because you have to convey the same sentiment just using your voice. It is a different skill you are using.
"You do have the liberty to interpret a line a certain way and then immediately do it a different way."