It's a fairly unknown fact that every human has a death frequency, a sound which will kill them on the spot. Each person's frequency is different and the chances of them hearing it in their lifetime is less than one in a billion, but it does happen. Nearly all unexplained deaths can be explained by death frequencies. With enough time and the right equipment you could kill anyone your heart desired. The US government has spent billions over the years to trying to create a death frequency gun which can detect a person's achilles frequency in seconds and render them dead. So far their advances have been laughable. Sadly for one death-row test subject, his death frequency was the sound of his own smug laughter.