With surveillance technology getting better and better, it’s harder than ever to keep secrets from leaking through the set of a big new TV show or movie. Marvel Studios is an old hand at it by now; they encrypt scripts sent to actors, shoot down drones fans send to spy on the set, and more.

HBO did a lot of this spoiler-spoiling back when Game of Thrones was on. Emilia Clarke, who played Daenerys Targaryen on Game of Thrones and plays the Skrull alien G’iah on the new Marvel series Secret Invasion, has been up close and personal with this stuff for years.

“When we were doing Game of Thrones, when it started to get to the later seasons, some massive security changes happened,” Clarke told Entertainment Weekly. “I was chatting with [showrunners] David [Benioff] and Dan [Weiss] and they were like, ‘Marvel. We’re just learning from Marvel. Whatever Marvel’s doing, we just want to do that.’ So that became, you don’t print anything — and then there was like me and Peter Dinklage being like, ‘I need it on paper! I can’t learn my lines without it being on paper!’”

Game of Thrones copied Marvel’s strategies for preventing spoilers

But even with all this experience, the shroud of secrecy around a Marvel set still intimidated Clarke. “I was like, ‘I think a man’s going to come and kill me if I say anything,’” she recalls, adding that she even took the SIM card out of her phone for the first few days of filming because she was so afraid of people finding her. She was determined not to be the source of any leak, since she remembered how much it hurt when things leaked from the Game of Thrones set. “It just sucks,” she said. “Not that I did the spoiling.”

At this point, she seems to have found a groove. “I’ll tell you what, it’s so much easier now because whenever it comes up or people want to ask, you just get to be like, ‘Dude, Marvel. I can’t say anything,’” she said. “That’s just what I kept saying over and over again.” If it works, it works.

Taking a hard line is best, because people will go to great lengths to leak Marvel secrets, as Secret Invasion star Samuel L. Jackson recalled. “I remember when we got ready to do Avengers, someone printed out a copy of my Avengers script that had my watermark on it, and put it online for sale. I was shooting in Canada and Marvel came to Canada. It had been printed in the production office… They found out who it was, dude quit, left the country. They set up a fake buy for the script, dude didn’t show up. It was crazy.”