The 25-year-old British actress, who stars in new horror movie "The Wolf Man," found it impossible to make the high-pitched shrieks required during shooting and resorted to "heavy breathing" to sound frightened.
The actress told Empire magazine: "I'm not a great screamer. I don't have a good upper range. I'm sure they're going to have to dub me with someone who has better lungs - or more feminine lungs, at least! I just did a lot of gasping and heavy breathing, which might have to do."
Emily confessed that although vocally she felt rather masculine while making the movie, she felt like a "wuss" when her character had to run. She explained: "It's also impossible not to run like a girl. You have to run like a girl in a long skirt and a corset. And I'm not bad on a treadmill, I don't look too awful, but I do in this film. I look really, really, wussy."
Emily - who dated Canadian singer Michael Buble for three years before their 2008 break-up - has previously said she doesn't fit in with the glamorous Hollywood lifestyle, because she dresses too scruffily.
She said: "I like fashion, I'm very partial to Marc Jacobs and Prada, but I don't want clothes to wear me. Ordinarily, I dress like a teenage boy in layered T-shirts and Converse gear."
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