We're not talking about disease or some sort of virus. Imagine a marksman hiding behind a bush, sighting his weapon on an unwary foe. He squeezes the trigger. The foeman is talking with his comrades when he suddenly jumps and falls down dead. Puzzled, his comrades roll him over and much to their surprise, see blood pouring from him. Looking around, no smoke is seen and as no shot was heard, they grow uneasy and run as another of their number soon falls dead to the silent killer. Fiction? No, it's silent killing with an airgun in the flintlock era before the 19th Century. It would take another fifty years before a reliable repeater would be produced and about a century before silenced firearms were feasible.
Click here and go to the Girandoni Airgun video.