One of Jurassic Park’s most memorable details, whether you’re talking about the original movie or the whole series, is the roar of the Tyrannosaurus Rex. When those cables snap and the predator escapes its pen, it sets the tone for the rest of the film.

Source: Jurassic Park (1993), Amblin Entertainment

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Naturally, as the culture is obsessed with the artifice behind the spectacle, people have wondered ever since 1993 how they did it, and years later they would get their answer.

The team responsible for the bellowing sound effect was led by sound designer Gary Rydstrom and he divulged the inside baseball of how his crew came up with something out of nothing for an extinct animal no one has ever heard or encountered.

Rydstrom explained to NPR in 2013 that they started by mixing several incongruent sounds from the animal kingdom together – from a baby elephant to a tiger and an alligator. “We started recording all kinds of weird animal sounds,” he said.

Source: Jurassic Park (1993), Amblin Entertainment

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“I tried to get every interesting animal recording we could find, not even caring right away what they would be for,” he’d add. “Then you try to sift through [the recordings] in the studio and see what’s interesting.”

Rydstrom also had a little fun with the standard procedure of playing with the sounds’ pitch and frequency. “One of the fun things in sound design is to take a sound and slow it down. It becomes much bigger,” he explained to Vulture in 2015.

According to a behind-the-scenes book, The Making of Jurassic Park: An Adventure 65 million Years in the Making, the elephant squeal, the gator gurgle, and the tiger snarl were mixed to create the otherworldly screech of the Rex.

Source: Jurassic Park (1993), Amblin Entertainment

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The baby elephant’s sound in particular was integral even though it only made the desired noise once. “We kept trying to get it to do it again [a cute high-pitched scream], and the handlers were saying, ‘We never heard it do that before; that’s a weird sound,’” Rydstrom said.

It was important to get the right sounds. Everything had to be in order for the scene when the Rex escapes and is fully revealed. “I think maybe other directors would have had a shock moment where you see the T. rex show up out of the blue,” Rydstrom clarified in a commentary track.

“Spielberg was great in the T. rex scene by getting several minutes of tension because you knew what was coming. And you knew it because you heard it before you saw it. It’s nice when movies think about sound that way,” he continued.

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Rydstrom, Steven Spielberg, and the T-Rex made cinematic history in that moment and won an Oscar for Best Sound Effects Editing, Best Sound, and Best Visual Effects.

However, based on recent findings, the roar they composited wasn’t even close to accurate as inventive as it was. Scientists now say T-Rexes probably did not roar at all as they are more closely related to birds than they are most land animals.

Their vocalizations are likely much closer to ostriches and emus – hoots, coos, and the occasional boom with their mouths closed – as dinosaurs lacked the vocal organs found in people and birds.

Source: Jurassic Park (1993), Amblin Entertainment

Unlike Jurassic Park, shockingly, the noises dinos, especially Rexes, make are believed to be low-bass vibrations you wouldn’t pick up auditorily despite their massive size. If you did, you’d feel it in your bones first – and by then it’d be too late.

For illustration, YouTube kaiju nerds DangerVille made a video demonstrating what a T-Rex could sound like in real life, and we warn you, it’s pretty chilling.

The roar we know returns in Jurassic World Dominion this June.

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