Emma Watson has explained why she no longer always says yes when fans ask for selfies.

The Beauty and the Beast star says that for her it’s the “difference between being able to have a life and not” and once someone snaps a selfie with her, people are immediately able to find her location.

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“For me, it’s the difference between being able to have a life and not,” Watson told Vanity Fair. “If someone takes a photograph of me and posts it, within two seconds they’ve created a marker of exactly where I am within 10 meters.

“They can see what I’m wearing and who I’m with. I just can’t give that tracking data.” Watson went on to explain that declining selfies doesn't mean she’s not up for fan interaction, instead she’d rather have a chat than pose for a picture.

“I’ll say, ‘I will sit here and answer every single Harry Potter fandom question you have but I just can’t do a picture’ ”—and much of the time people don’t bother,” she continued.

“I have to carefully pick and choose my moment to interact. When am I a celebrity sighting versus when am I going to make someone’s freakin’ week? Children I don’t say no to, for example.”

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Speaking about the passion of Harry Potter fans, Watson added: “I have met fans that have my face tattooed on their body. I’ve met people who used the Harry Potter books to get through cancer.

“I don’t know how to explain it, but the Harry Potter phenomenon steps into a different zone. It crosses into obsession. A big part of me coming to terms with it was accepting that this is not your average circumstances.”