" Infrasound is not heard, it is felt. Infrasound holds a terrible secret in its silent roar. Infrasound produces varied physiological sensations which begin as vague “irritations”. At certain pitch, infrasound produces physical pressure. At specific low intensity, fear and disorientation. Nazi propaganda engineers methodically used infrasound to stir up the hostilities of crowds who were gathered to hear their madman. The results are historical nightmares."
http://journal.borderlands.com/1996/the-sonic-weapon-of-vladimir-gavreau/