The xenomorph from the Alien franchise is one of the most legendary creatures in cinema history. Now it’s the star of FX’s series Alien: Earth too.

Many filmmakers have put xenomorphs on screen and many composers have written music for them. Alien: Earth’s Jeff Russo may be the first to use the Aztec death whistle, as he explained at Deadline’s Sound & Screen Television awards-season event.

“The Aztec death whistle was just something that my engineer, Michael Perfitt, brought into the studio one day,” Emmy winner Russo said. “I went behind the glass and played it a couple times. It became very evocative of the stress and tension one might be under when faced with a xenomorph.”

The Aztec death whistle may have the best name, but it’s not the only exotic instrument Russo uses. “There’s this bassdesmophon made by a company in Switzerland I had built for this particular purpose,” he told the crowd at UCLA’s Royce Hall. “It’s a very evocative, guttural sound.”

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Alien: Earth stars Sydney Chandler as Wendy, a dying child transferred to a synthetic body. When her brother (Alex Lawther) discovers her new form, Russo was challenged to craft a sibling love theme.

“That’s a delicate fine line to play because it’s emotional but there’s no romance,” Russo said. “It’s not romantic. it needed to walk that line.”

Alien: Earth creator Noah Hawley follows in the footsteps of Ridley Scott, James Cameron, David Fincher, Jean-Pierre Jeunet and Fede Álvarez in the movie series. Similarly, Russo doesn’t forget the scores by Jerry Goldsmith in Alien and James Horner in Aliens.

“There are little things I wanted to call back to,” Russo said. “There’s a delay with the horns that happens in a lot of places. The way [they] built tension with high strings, give a little bit of that to the score but also trying to create something that is unique for us since this is the first time the story’s ever been told on Earth.”

Russo has read seven of the eight scripts for the upcoming Season 2.

“Noah knows that once he sends me those scripts I’m going to start thinking about it and writing and formulating a plan for the next chapter,” Russo said. “I’m now trying to formulate what that is. I sit down in my studio and bang stuff out on the piano before I try to write.”

He is hopeful for more creature themes, including the eye monster that is original to the series.

“I didn’t get a chance to write a theme for our Eye Midge,” Russo said. “I haven’t gotten to write one for that particular character, but I’m hoping in Season 2. I’m sure the Aztec death whistle will end up in Season 2.”

Check out the panel video above.