"If people knew where the sounds in Jurassic Park came from, it'd be rated R!" Gary Rydstrom, the sound designer for the original 1993 film, told Kyle Buchanan at Vulture. "It's somewhat embarrassing, but when the raptors bark at each other to communicate, it's a tortoise having sex."

Faced with the rather difficult task of 'voicing' creatures whose voices no human has ever heard before, Rydstrom went to nature for the answers.

The Gallimimus flock was voiced by squealing female horses on heat. The Tyrannosaurus Rex was voiced by Rydstrom's Jack Russel terrier, Buster, and a baby elephant. And yep, the raptors were voiced by hissing geese, and in that famous kitchen scene, a mating tortoise. You can hear it at the 14 second mark:

Rydstrom told Buchanan that mating tortoises are kind of the perfect source for a sound designer, because they can mate for hours and hours, and all the way through, they make these peculiar barking noises that sound nothing like what you'd think a tortoise would sound like. 

Want to have everything you hold dear ruined in one fell swoop? Watch this to the end, and then someone invent something that can erase sound memories from my brain, because that was all too real.

Why do they make such odd noises when they mate? It's not entirely clear, but tortoises are generally pretty vocal creatures, equipped with an entire repertoire of grunts, hisses, barks, squeaks and sighs for every occasion, whether they're fighting with a rival male or ramming a female in one of their typically violent pairings. 

When a male tortoise has his sights set on a female mate, he will circle her aggressively, nipping at her feet and shell, and ramming into her until she's trapped. She'll be mounted, and then it's the male's job to successfully deliver his sperm without tumbling off the back of her shell - a task easier said than done, as Rydstrom soon found when he was recording them. The whole process is pretty unpleasant for the female, and her shell can even be damaged by the activity. 

For the males, this is something they've literally been waiting an entire decade for - sometimes even longer. Because some species of tortoise can live for hundreds of years, they take a long time to reach sexual maturity, compared to other animals, including humans. The Galapagos tortoise, for example, doesn't develop proper reproductive organs until it's 15 years old, and it can wait another 10, 15, or even 25 years before it's able to actually use them. And the Aldabra giant tortoise, which can live over 250 years, doesn't hit sexual maturity until it's 20 or 30 years old. No wonder they sound so excited about it. 

Here's Sir David Attenborough narrating a beautiful moment between a tortoise and a shoe:

Source: Vulture