'Edge of Tomorrow' star Emily Blunt discusses her new action movie

What's more scary, fighting aliens with Tom Cruise or singing in front of Meryl Streep and Johnny Depp?

Both brought butterflies to Emily Blunt's stomach, which is how the actress knows when to take a role.

"I like asking myself, 'How on earth am I going to do this?'" Blunt said as she sipped an iced latte at a coffee shop in the artsy L.A. neighborhood of Los Feliz.

In her latest film, "Edge of Tomorrow," she wields big guns – of the biceps and military-style variety – as Rita Vrataski, tasked with turning Cruise's character from a scared pencil pusher to a skilled warrior.

"In these male-fueled genres, it's usually the woman who's holding the hand of the guy and he's running through explosions leading her, and I wanted to be doing the leading," Blunt said. "This was the extreme idea of what I ever thought I'd want to do."

Her background is in theater – she made her professional debut on a London stage in 2002 opposite Judi Dench. Blunt's big-screen breakthrough came four years later in "The Devil Wears Prada" as a chilly magazine assistant. She has since appeared in more than 20 movies.

But none prepared her to be an action star. What did was three months of rigorous training in martial arts, weapons and wire work; and working with Cruise, who famously does his own stunts. ("I didn't want him to be the only one showing off," she laughs.) Blunt wore a weighted vest to prepare for the 85-pound armored "Exo-Suit" she wears in the film. She nearly broke her nose – demonstrating for a reporter how the on-set physician straightened it with a finger in each nostril and a quick, painful shift – and may have permanently damaged her thumb.

The training helped her become Rita, and taught Blunt about herself.

"I think it did toughen me up in a big way," she said, "because now I know what I'm capable of."

Director Doug Liman said Blunt's character is "the hero of the movie."

"Emily's performance is even more impressive when you step back and see that she dominates the screen against the biggest movie star in the world whose character also happens to have a superpower," he said.

Blunt's next role demanded a different sort of bravery: singing on screen. Blunt, Streep, and Depp star in Rob Marshall's dark musical fairy tale, "Into the Woods," due in theaters on Christmas Day. She worked with a singing coach to prepare for her role in the Stephen Sondheim adaptation.

Besides training, Blunt draws on her deep love of people to inform the characters she plays. An avid reader, she finds that discovering characters on the page inspires her when she creates them on the screen.

"When I choose to play a character, it's because I love that human heartbeat that they have and I've found an 'in' with them," she said.

Disconnecting from Hollywood is part of the process. Blunt recharges at home with her husband, actor John Krasinski, and their 3 1/2 -month-old daughter, Hazel. The couple likes to entertain, and Blunt cooks Italian dishes and a few from her homeland ("English food is underrated," she said).

That source of off-camera love and stability allows Blunt to weather Hollywood's whims and follow the butterflies when a challenging role beckons.

"It's such an unknown, this business," she said. "You don't know when you're next working, you don't know who're next playing, you don't know who you'll next be working with, so I do believe you've got to walk into each day with great hope."