It's all about protecting what she has with American actor fiancé John Krasinski, she explained.
"Don't be a Chatty Cathy about [the relationship] – I think that's the secret," the 26-year-old actress told the Popeater website
"You have to have a dual existence…You have the acting side of it and the business life.... and then you have your private life and your downtime…
"You have to make that 'divide'…and make it clear to you."
And she was certainly sticking to her guns at the premiere of her latest movie, The Wolfman, on Tuesday night.
The 26-year-old actress, who stole the show in an exquisite deep blue Kaufman Franco dress and Matthew Williamson belt, had husband-to-be John right by her side on the red carpet.
But the only man she had anything to say about was co-star Anthony Hopkins.
“He’s very, very cool. I was riveted by him. I would sit around and talk to him between takes, and he’d tell us wonderful stories," she said.
Set in the 1880s, the horror remake stars Emily as the fiancée of a missing man who lures his brother, played by Benicio del Toro, back home to help look for him.
Upon his return to the sleepy hamlet, del Toro soon discovers something with an insatiable bloodlust has been killing the local villagers.
The movie is set for release in the UK this Friday.