The Hostel filmmaker was travelling in the South American forest on a scouting trip, when he came across a group of villagers - with no electricity or running water - and asked them to appear in his latest project about cannibals.
He tells Movieline.com, "We said, 'Can we shoot here?' and talked to them, and our producers said, 'We have to explain to them what a movie is. They've never seen a television.'
"So we brought a generator and set up a television. I thought they were going to show them (family classics) E.T. or The Wizard of Oz, but they showed them (horror movie) Cannibal Holocaust to see how much they could handle. The villagers thought it was the funniest thing they'd ever seen."
Roth and a small movie crew then filmed a couple of practice shots to see how the natives would react on camera - and the Inglourious Basterds actor admits the group did great: "Because none of them have ever owned a camera or had any photographs of themselves and no conception of what television or movies are, they're so natural and relaxed. They're amazing. They're not even conscious of what (the camera) is doing to them.
"I have a whole village full of kids that are funny as hell that will have cameras all over and not even think twice about it. They don't get nervous, nothing."
In exchange for their services, Roth and the production team have agreed to buy the villagers a boat, adding, "We're giving them a motorboat - that's the deal. And we're giving them medical supplies and school supplies, so they're ecstatic. The one thing they need is a boat. They were like, 'This will literally change our lives.'"