'Scariest sound of the world' was final thing people heard before they were murdered

Described as the 'scariest sound of the world', this 500-year-old noise is still sending chills down people's spines.

Dating back to around 1250 to 1521 AD, the terrifying sound is known as the Aztec Death Whistle, or Skull Whistle, which is made from an unusual music instrument that was found in grave sites of the time.

The instrument was in a skull-like shape, which archaeologists were left perplexed by, until one blew in the top of it, creating one of the world's most deeply unsettling sounds.

The horrific sound was played to volunteers (Tanner Pearson/The Boston Globe via Getty Images)

In fact, the resulting sound was a piercing screech, which can be compared to desperate human screams, creating one of the most eerie sounds ever.

A mix of a thousand screams and a haunting gust of wind, it turns out that the people of today, and not just the Aztecs, are spooked out by the noise.

This new study has looked at the reactions of people when the sound was played, specifically how their brains responded.

Experts think that the whistles could have been historically used during battle or to scare victims during human sacrifice rituals, though this is unconfirmed, as Lead author Professor Sascha Frühholz said to MailOnline: "The sound is rough and high-pitched, and as listeners, you usually do not like such sounds."

The study got volunteers that hadn't heard the noise before to listen to it for the first time, with their response being noted.

Professor Frühholz went on: "Since the Aztec skull whistle sounds close to a human scream, we wanted to investigate if humans have the same negative and aversive response to Aztec death whistle sounds."

The European participants were played genuine Aztec Death Whistles, replicas, the researchers own whistle, and some other sounds.

Using functional magnetic resonance imaging (fMRI), their brain activation was monitored, as they were asked to describe what they heard and what it made them feel.

Overall, it looked like it provoked a negative emotional response, along with a sense of urgency, while many compared it to firearms, shouts of fear, and angry voices, among other things.

It is theorised that the instrument was made to mimic sounds like screams.

Studies in the past found that the resulting noise comes as a result of multiple tones being played at once, while the exact sound can be found in 'terrifying music', creating a 'terrifying' sound.

The scary looking instrument makes a horrific racket (Robert Och/Getty Images)

When asked to come up with a description of what it sounded like, most quickly drew similarities to the human scream, while other answers mentioned chainsaws, trains, or even kettles.

This paper was eventually published in Communications Psychology, while the researchers think that the mix of natural and unnatural sounds makes the sound so eerie.

"With fMRI we found that the sounds have both an affective [emotional] nature and they have a more abstract and symbolic nature, which triggers associative mechanisms in the brain," Professor Frühholz added.

One listener had a flurry of activity set off in their brain's auditory processing regions as it attempted to figure out the origins of the sound.

In the end, it would confuse and stun the brain, which is why the Aztecs may have used this shock to evoke fear in people.

Archaeologists are unsure about who they were primarily used for, but as it is so scary and frightening, Frühholz and his team have drawn it up to the ritual explanation.