They discovered that the whistle triggered basic psychoaffective affects while also activating areas of the brain associated with symbolic meaning.

Sound has the incredible ability to instill a certain kind of emotion into whoever hears it. The soulful call of a loon feels melancholy, the roar of a lion inspires danger, and the screech of an Aztec death whistle -- utter terror.

First discovered during a 1999 excavation of an Aztec temple in Mexico City, clutched in the hands of a beheaded 20-year-old sacrificial victim, these whistles -- also known as ehecachichtli -- are commonly associated with sacrificial ceremonies and are often adorned with skulls or owls, which symbolize the coming of death. The most stunning feature of these whistles, however, is their distinct, unsettling screech that appears to mimic a human scream.

Now, a new study from the University of Zurich reports that the Aztec Death Whistle is unlike any instrument ever made. Literally.

The researchers analyzed the acoustic properties of the whistle by creating 3D digital reconstructions and physical clay replicas from original death whistles on display at the Ethnological Museum in Berlin. They also tested the psychological reaction of listeners by recording their brain patterns -- a field known as psychoacoustics (a most excellent death metal name). The results were published earlier this week in the journal Communications Psychology.

"The whistles have a very unique construction," Sascha Frühholz, the lead author of the study, said in a press statement, "and we don't know of any comparable musical instrument from other pre-Columbian cultures or from other historical and contemporary contexts."

The construction of these unsettling whistles is somewhat complex. The body of the whistle holds two opposing chambers that are each constructed to disturb airflow and create the whistle's tell-tale screeching sound. As Ars Technica notes, these whistles leverage the concept of the Venturi effect, as air speeds up while moving through a narrow passage.

To test the effect of the death whistle on listeners, the researchers had 70 subjects rate a sample of 2,500 sounds. From that data, the team found that the death whistle was mostly closely associated with negative emotions and natural sounds, like primate screams. A further study (which scanned the brains of 32 participants using fMRI) found that as people listened to the death whistle, it activated an area of the brain associated with symbolic meaning. This means the whistle not only had an overall negative response, but also produced the idea within the minds of the listeners that the sound was symbolic. The researchers describe this as a "hybrid nature" of the whistle -- providing a basic psychoaffective influence while also triggering symbolism.

"This is consistent with the tradition of many ancient cultures to capture natural sounds in musical instruments, and could explain the ritual dimension of the death whistle sound for mimicking mythological entities," Frühholz said in a press statement.

In other words, that horrific screech is a feature -- not a bug.