“Thirteen Lives,” a new film by Ron Howard about the Tham Luang cave rescue, represents an attempt to give Hollywood a chance to embrace one of the most dangerous rescue missions in recent memory. Production meticulously recreated the Tham Luang caves, where twelve youth soccer players and their coach were trapped underwater. As a result, stars like Colin Farrell were reportedly terrified of what they were about to experience.

“Terrifying in a word. Terrifying,” Farrell told Entertainment Tonight. “It really was. It was scary. I’m not a great swimmer anyway, not that we were swimming, not that we were treading water, we had to stay on the surface, but they built a really impressive network of caves, it was about four or five different caves that were based on the topography of the caves, the Tham Luang caves in Thailand, and they filled them full of water, and we’d go down, and there was no up.”

As the film takes place in a cave, underwater scenes were filmed indoors in the dark. So it wasn’t the water that scared me, but not being able to see where it ended.

“There’s a lot to be said for being able to look up in the water and see the surface,” he said. “So when you can’t, and there’s actually a ceiling over your head, and there’s no air at all, it just wreaks havoc on my mind.”

Even with the help of a skilled safety team and several consultants involved in the rescue, Farrell suffered panic attacks.

“We had amazing assistants,” he said. “We had Rick Stanton there, we had Jason Mallinson, who were two of the gentlemen who were part of the five that swim the team out, but man, I had panic attacks underwater; that’s a new experience. A panic attack underwater is a new experience for me.”

Continuing: “I mean, at the end of the day, we did have amazing safety divers and a team of safety divers, but I asked one of the safety divers on one of the days we werehe spends a lot of time in the tanks floating and talking when we weren’t shooting I said, ‘How many films have you done,’ and the safety diver said, ‘About twenty underwater films.’ I said, what was the most dangerousand you know where this is goingthey went, ‘This one.’

“Thirteen Lives” plays in select theaters now and will stream on Amazon Prime starting Friday, August 5. 

When Colin was filming, he suffered a panic attack.