A new sonic weapon being developed for the Pentagon makes use of one of the most fearsome sounds known to humans: a baby crying. Once aimed at the enemy, a focused beam of the familiar noise, played backwards, will be painful enough to make enemy soldiers run for their lives, according to its developers. They call it the ��sonic bullet��. There are 50 soundtracks to choose from, and they are played at 140 decibels. That is akin to standing beneath a passenger jet as it takes off. Hardly surprising, then, that the weapon causes an intense headache in its victim.