Could the principle of owls' silent flight be used for stealth aircraft?
Their primary wing feathers have an unusual structure incorporating a fringed, comblike leading-edge, which reduces wind noise.  The wing feathers also have an overall softness or flexibility.  The trailing-edge of the wing is also dominated by soft, fringed edges.  Even the underwing lining (covert) feathers have an unusual softness that plays a role in sound suppression.

See for example --
https://www.owlpages.com/owls/articles.php?a=7n ,
https://animals.howstuffworks.com/birds/owl-fly-silently1.htm .
Google "owl feather structure" for more.

I'll leave it mostly unsaid, as to whether any of these features are worth incorporating into a jet-powered aircraft.  Maybe some of these features might be applied to the intake or exhaust areas, in a more rigid metallic form?