CNN article on Ancient Aztec Whistles of Death. I listened to the example track (the link in the text near the bottom of the picture), and I had my headphones on pretty loud, and the first one scared the crap out of me so much it dumped seven tons of adrenaline into my alligator brain and I literally tore my headphones out of my ears. Maybe part of that reaction was surprise and decibels too but... *shudders* I'm going to have to wait a while before going to sleep now...