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It's almost Halloween -- a good time to look at the science behind the sound of fear

STEVE INSKEEP, HOST:

OK. It's almost Halloween - that one day a year you are encouraged to take candy from strangers, and that one time of year when people decorate their yards with ornaments designed to scare you.

(SOUNDBITE OF SCREAM)

INSKEEP: There's a science behind that sound of fear, and this is a perfect story for the radio, so NPR's Nathan Rott is on it. He reports you have to start with yellow-bellied marmots.

(SOUNDBITE OF MARMOTS SQUEAKING)

NATHAN ROTT, BYLINE: I first met Dan Blumstein at a research station high in the Colorado Rockies. This was a few years ago.

How many marmots would you say you've trapped over the course of your career?

DAN BLUMSTEIN: A lot (laughter). We have about 1,000 captures a year in this valley.

ROTT: Blumstein is a behavioral ecologist and conservation scientist at UCLA...

(SOUNDBITE OF MARMOTS SQUEAKING)

ROTT: ...Where he leads one of the world's longest-running studies on a wildlife population, yellow-bellied marmots - ground squirrels about the size of a cat, stubbier legs.

BLUMSTEIN: You interview people. We interview marmots.

ROTT: (Laughter) So why is it making that noise?

BLUMSTEIN: This one's alarm calling. They can alarm call...

(SOUNDBITE OF MARMOT ALARM CALL)

BLUMSTEIN: ...Pretty much from the first days they emerge from their burrow.

ROTT: Similar to how birds or squirrels might chirp, warning to others when you're out walking your dog. But it was a different sound that really got Blumstein thinking about fear. One day, when he was gently cradling a baby marmot, it screamed.

(SOUNDBITE OF MARMOT SCREAM)

BLUMSTEIN: And I was sort of shocked by this scream and almost dropped this animal. I had this emotional response to the scream.

ROTT: Which made him curious - what makes screams so alarming, so different than normal alarm calls?

BLUMSTEIN: So I started reading and learning about screams.

ROTT: Listening to recordings of other animals, to screams in horror movies.

BLUMSTEIN: Janet Leigh's first scream in "Psycho," in the shower scene...

(SOUNDBITE OF FILM, "PSYCHO")

JANET LEIGH: (As Marion Crane, screaming).

BLUMSTEIN: ...That's a real scream, the first one. You know, it's throaty. After that, it became, you know, good actor screams.

ROTT: A real scream, Blumstein found, whether it comes from an actor or a marmot, happens when a mammal overblows its vocal folds, pushing air through their throat and their mouth faster than normal.

BLUMSTEIN: And if you make a spectrogram, a voice print of these sounds, what you see what are considered nonlinear attributes.

ROTT: Irregularities - the kinds of disjointed noise your car stereo makes when it's turned up too loud, or if I talk too loud into my mic.

BLUMSTEIN: That bad is predictably bad. And it involves a whole suite of acoustic, you know, things that occur when a system is sort of above its normal operating threshold.

ROTT: And it's what makes irregular noises so unnerving, so impossible to ignore, to just about any animal that hears them.

BLUMSTEIN: You can play back nonlinear sounds to even animals that don't vocalize, like skinks and lizards, and they respond differentially to the noisy stuff.

ROTT: Meaning the sound of fear is widely recognized in the animal kingdom. It's supposed to get your attention. It's supposed to scare and alert you.

BLUMSTEIN: We are who we are because of who our ancestors were - and not just our primate ancestors, but across the lineage of life.

ROTT: So, Blumstein says, if a noise scares you this Halloween...

BLUMSTEIN: We should embrace our inner marmot and be happy that we're scared by those things.

ROTT: Because it's what helps connect us to the rest of the world.

Nathan Rott, NPR News.

(SOUNDBITE OF SANTANA SONG, "BLACK MAGIC WOMAN") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Nathan Rott is a correspondent on NPR's National Desk, where he focuses on environment issues and the American West.