I have taken a shot on a deer with a slick trick that did hiss with my set up. In fact, it was looking at me when I released...and it didn't make a move until after the shot arrived. Who knows, if properly researched, they may find the hissing/humming noise actually stimulates the deer's curiosity and tends to keep it from jumping the string. Think like a deer; you just heard the slap of a bow string and your instinct tells you to get out of dodge but as you start your escape, you hear a hissing noise...and then it hits you.