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.
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