February 02, 2017 at 06:14 AM EST

Part of the reason director James Gray (The Immigrant) wanted to take on the challenge of adapting The Lost City of Z, David Grann’s hit nonfiction book from 2009, was because it would be just that — a challenge.

“If somebody tells you you’re not going to be able to do it and how hard it is and why would you want to do it, that’s the thing that always drives me toward something,” Gray tells EW.

And the shoot, which took Gray and star Charlie Hunnam to remote areas of Colombia for five months, was hard. But soon, you’ll be able to see the fruits of that labor when The Lost City of Z — also starring Robert Pattinson, Sienna Miller, and Tom Holland — hits theaters April 14 and expands on April 21. Check out an exclusive new trailer for the film above (and a new poster below), but before watching, sample one of Gray’s stories from the shoot that gives a glimpse at the work that went into it.

“We were all in the river, and we were about up to our knees. The water was very shallow there. It was so hot. It was about 100 degrees with 100 percent humidity, just punishing. We were all out there, and I think I had three cameras going. I was behind camera A, which is usually the case. I was watching the take, and then all of the sudden, out of the corner of my eye, I saw something distracting run up the side of the river. I thought, ‘That can’t be a crocodile. There are no crocodiles here.’ So I went up to the guide, who was — by the way — wonderful, I went up to him and asked, ‘Are there crocodiles in this water?’

‘No, Mr. James, no crocodiles. No.’

We do another take. The actors are working. Behind the actor, I see it in the water: an eye lurking in the water with its snout. ‘What is that? I see it. That’s a crocodile,’ I said to the guide.

He said, ‘No, Mr. James. Not a crocodile. That’s a black caiman.’

I don’t know why I accepted this at the time. I thought, ‘As long as it’s not a crocodile,’ even though it looked like one. We saw them every now and then, and I said, ‘Well, no, it’s not a crocodile. He told me it’s a caiman.’ So of course, I come back to L.A., and I read that the black caiman is a crocodile, but actually more dangerous than a crocodile. We had been shooting in all of that stuff in what were essentially crocodile-infested waters.”

You May Like