There are some sounds the human ear was never equipped to hear. The 'silbato de la muerte,' a.k.a. the Aztec death whistle, makes one of those sounds.
I've honestly never heard a horror movie sound effect more chilling than this - like the white noise of the waking dead, the dry wail of demons being flayed alive...
Pretty frightening, huh?
According to death whistle expert Roberto Velázquez Cabrera, the original purpose of the instrument is hard to define, though it's suspected that it was used for rituals to do with death, and possibly even human sacrifice.
The festival of Toxcatl involved a young man split open with an obsidian dagger, his heart and head removed, his skin flayed and his flesh consumed by the highest ranking citizens.
Historian Lewis Spence described this sacrificial youth carrying the death whistle in 1913...
A youth was slain who for an entire year previously had been carefully instructed in the role of victim... He carried also the whistle symbolical of the deity [as Lord of the Night Wind, Tezcatlipoca], and made with it a noise such as the weird wind of night makes when it hurries through the streets.
The more you know, eh? Try listening to the death whistle again before you go to sleep tonight... sweet dreams.