Owls are majestic nocturnal predators. One of their best weapon against an unsuspecting prey is their near silent flight. The incredible result of the evolution of their wing and feather structure makes it possible for them to swoosh by so that what little sound they make can only be heard once they have passed and left you one meter behind.
The silence was a mystery for a long time. Until 1934 a pilot and an ornithologist Robert Rule Graham combined his two passions and came up with the so called "three traits paradigm". This includes the comb structure at the front of the wings, a velvety soft cover of feathers and raggedy fringe on trailing the trailing edge of the wing. Further studies have shown that this might not even be all, but already those principles have been tried in attempts of making for example planes more silent.
The sound from a landing plane for example is not caused mostly by it's engines but the air rushing past it's figure. By applying the principles learned from the owl wings can have as dramatic effects as bringing the noise down by 10 decibels. Of that doesn't sound impressive remember that the desibel is a logarithmic scale. So lowering the noise by 10 desibels means the noise will be only half as loud as before!