Reese Witherspoon takes on her sexiest role yet in the spy comedy, “This Means War,” and the blond bombshell says she got a little help with her feminine wiles from the film’s director and her two handsome co-stars.

“It was actually interesting because between McG, Tom [Hardy] and Chris [Pine], they would tell me what men think is sexy, which is like, something I never really understood,” Reese told Access Hollywood guest correspondent Julie Moran of her “This Means War” schooling, during an exclusive interview backstage at the “Conan” show in Los Angeles on Tuesday. “I learned a lot, like they don’t like flats.

“Every time I wore flat shoes they’d be like, ‘That’s not sexy,’ and I have maybe 15 pairs of flats?” she continued. “They’re like, ‘Sorry, that’s just not going to work.’ So I literally, in every frame of the movie, I have heels on. Even the parts when I only had my underwear on, I still have my heels on!”

As for what Reese thinks is sexy, the 35-year-old said a good sense of humor is key, as “funny doesn’t sag,” something the actress once Glamour magazine.

“There [are] a lot of different ways to sort of get attention in this life and I think a lot of women sort of immediately get a lot of attention — especially young women — for how they look in a bathing suit or how they look sexy on the cover of a magazine,” Reese explained. “But to me, what’s really appealing about a woman is her sense of humor, being able to laugh at yourself, intelligence, your opinion about things that are going on in the world.”

Adding, “That’s what to me makes a woman beautiful and um and interesting. I think it’s more important to be interesting and endlessly curious than anything else.”

Reese, who took home the Best Actress Oscar for her portrayal of June Carter in 2005’s “Walk the Line,” revealed that fans will soon get another chance to hear her sing – this time, in a Nora Ephron-helmed Peggy Lee biopic.

“We are definitely working on Peggy Lee, yeah,” Reese confirmed. “It’s a story that’s very dear to my heart — I know her family very well. They approached me about playing [Peggy] in a movie and we’re working on it.”

Check out Reese, Tom, Chris and Chelsea Handler in “This Means War” – in theaters on Friday.