Have you ever used a fibre-tip pen? Noticed how they squeal and squeak in a terrible way? My theory is that the tiny fibres, which are hair-like, resonate at their natural frequencies. This amplifies the noise up, until you can hear it. Upon reaching your ears, the tiny hairs in your ears react. Now, due to the way in which your ears work, rows of these hairs exist, at various different lengths, so the sound hits them, and causes resonance at the frequency of the incoming sound. This tiny movement is then turned into electrical signals, and the brain interprets these. So, when you use the fibre-tip, the tiny squeaks set up nasty resonances in a few of these sensitive hairs, causing you to flinch as the sound upsets your brain, which isn’t used to such a narrow band of frequencies, and so few of the hairs being stimulated so hard, without the other hairs close to them being tickled as well. Sort of like being hit by an audio laser.. If this theory is correct, then this could be used as a non-lethal weapon for disruption of demonstrations and the scaring of feral animals.