A Hiss, and a Scream: The Reason Aztec Skull Whistles are so Scary

Musical instruments are near universal across all cultures, ancient and modern, but the music they make is not always pleasant. Aztec skull whistles, extremely versatile instruments from 500 years ago, are certainly not.

Such whistles were used for more than 250 years from around 1250 AD by the Aztecs of Central America, producing a combination of eerie hisses, honks and screams. But it has never been clear what purpose they served.

However a new study by Sascha Frühholz, Pablo Rodriguez, Mathilde Bonard, Florence Steiner and Marine Bobin and published in Nature may have the answer. By analyzing the psychoacoustic and archeoacoustic nature of these ancient skull whistles, they have shed light on the impact listening to them might have on an individual.

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The team have found that the combination of sounds produced by the whistles provoke a strong psychoacoustic response in a listener, and a negative one at that. People who hear the skull whistles describe them as “aversive and scary” and liken the sounds produced as “having a hybrid natural-artificial origin.”

The sounds are said to resemble a combination of indistinct voices and more prominent screams. They are particularly adept in mimicking threat sounds from our natural environment, ones which would naturally startle us and trigger a state of high alert.

The brains of listeners were monitored using neuroimaging techniques, which found that a human hearing such sounds are classed differently by our neural pathways, and that they are decoded by us in a different way to all other natural sounds. 

Along with the specific response triggered in the brain, our higher cognitive centers are triggered to make a recognition and threat assessment response to the sounds. These whistles are apparently directly tapping into the parts of our brain which respond to dangers.

So, what were the Aztecs doing with such nasty toys? Theories vary, with most pointing to the ornamentation and careful decoration on such skull whistles and concluding that they would have been used in Aztec rituals, a kind of musical accompaniment like a church organ if a church organ emitted bloodcurdling screams.

The “skull” on the skulls whistles might support this theory. It is often Mictlantecuhtli, the Aztec Lord of the Underworld, who is depicted: these might be the acoustics of a sacrificial death cult.

However other theories have also been presented for their use. Although they can be ornate they are also very small, no more than 5cm in most cases, and would have made an excellent psychological weapon for Aztec warriors to use while attacking an enemy. In the thick vegetation of the interior such whistles would also have created the illusion of a forest filled with screaming enemies, as well as keeping the warriors themselves within earshot of each other.

But perhaps the most interesting aspect of the study regards the intricacy of the skull whistles themselves. The sound produced is, through the design of the acoustic pathways within, very specific and non-linear, starting as a hiss and ending as a scream. The combination of the two manages to convey the strange overlay of something screaming in the distance, and something enormous and heavy moving nearby.

In the study, the skull whistle was playing alongside other sounds form nature, to assess what responses it provoked in a listener. Having heard these whistles, it is easy to understand why they are so scary.

For further information: Frühholz, S., Rodriguez, P., Bonard, M. et al. Psychoacoustic and Archeoacoustic nature of ancient Aztec skull whistles. Commun Psychol 2, 108 (2024). https://doi.org/10.1038/s44271-024-00157-7

Header Image: Aztec skull whistles produce a sound which elicits a fundamentally different response in our brains to other natural sounds. Source: Jennysnest / CC BY-SA 4.0; inset Frühholz, S., Rodriguez, P., Bonard, M. et al. Psychoacoustic and Archeoacoustic nature of ancient Aztec skull whistles. Commun Psychol 2, 108 (2024). https://doi.org/10.1038/s44271-024-00157-7.