When you hear the signature roars of Drogon, Rhaegal and Viserion — the three key dragon cast members in "Game of Thrones" — tortoise sex is probably the furthest thing from your mind. And yet, according to series sound designer Paula Fairfield, the mating cries of giant tortoises are among the many sound samples she used to give the show's great winged beasts a voice.

In a 2017 interview with RadioLab, Fairfield explained how she crafted the sounds of the dragons moving, roaring and communicating with other characters by mashing up various animal noises, including screeching birds and reptiles, fluttering dragonfly wings and even her own dog's nasal whistles. Listen closely to the way Drogon purrs in the company of his friends, and you may even hear a sound you'll wish you hadn't — the mating moan of a giant male tortoise. [Photos: 33 Stunning Locations Where 'Game of Thrones' Was Filmed]

First of all, yes, tortoises moan while they mate. The males, especially, are loud; Their mating groans can rattle on for 10 or 20 minutes, and can carry for miles around, James Gibbs, a conservation biologist at the SUNY College of Environmental Science and Forestry in Syracuse, New York, previously told Live Science. It's uncomfortable and a little funny to watch (here's a video if you're deathly curious), but a giant tortoise would probably say the same about your mating rituals.

So, why did Fairfield turn to this intimate corner of the reptilian soundscape for her dragon work? It's all a matter of imbuing each of the show's three dragon cast members with distinct personalities, she told RadioLab. Drogon, for example, is Daenerys' clear favorite. He is the rowdiest of the three, and yet the one Daenerys prefers to ride while flying about Westeros. He's even named after her "hot late husband" Khal Drogo, Fairfield said, so in a way "is like her lover."

"He's whistling at her all the time, he's whistling at her butt and saying, 'Ooh, baby,'" Fairfield said. "The groan of the male [tortoise] actually became, with some work and adjustments and stuff, the basis of Drogon's purr."

Fairfield added that the first time she watched the dragon-purring scenes with a larger audience, people couldn't help but giggle without knowing why. "To me, it's because [the purr] had that essence, that kind of sensual, sexual essence," Fairfield said.

You can listen for this tortoise essence while watching the final season of "Game of Thrones," which debuts Sunday (April 14).

9 Real-Life 'Dragons' in the Animal Kingdom5 Historical Inspirations for 'Game of Thrones'How to Survive the 'Game of Thrones,' According to ScienceOriginally published on Live Science.