It turns out that Game of Thrones used a bunch of drunken fans to create the scream of Viserion the ice dragon in Season 7.
Part of Daenerys Targaryen's brood of dragons, Viserion was mortally wounded in penultimate episode, "Beyond the Wall," and returned in reanimated form for the season finale to help the Night King bring down the Wall.
Tasked with creating a new sound for Viserion, one fan told Winter is Coming how sound designer Paula Fairfield came up with the zombified dragon's scream. Meeting a group of revelers from a bar in Chicago that regularly holds Game of Thrones screening parties, Fairfield asked them to scream on cue. As the fan told Winter is Coming at Con of Thrones in Dallas, "We just, like, took an evening, drank a fuck-ton of gin and screamed our hearts out, and sent ’em off."
However, Fairfield didn't reveal what she was doing with the scream until the season finale aired: "And then she came and watched the finale with us, she never told us what it was for. And then when it was all over, she leaned over and was like, 'You guys are the ice dragon.'"
The scene in question came towards the end of "The Dragon and the Wolf." With a skeleton crew left guarding Eastwatch by the Sea, an army of White Walkers marched on the Wall. The silence was then broken by Viserion's scream as he flew into battle with the Night King on his back.
Fairfield apparently used jackhammers and blowtorches to try and perfect the scream before she settled on inebriated fans to complete the sound. With the flying foe expected to be a big part of Game of Thrones' final six episodes, here's hoping Fairfield found some more drunken fans to record more of the dragon's scream for Season 8.