This sound is part of the wave of simple animal-noises-turned-memes that live on soundboards and WhatsApp forwards, where a single funny moo can be shared and reused endlessly. Long cow moos have long been a staple of comedy sound effects, used in cartoons and prank edits to undercut a serious moment with something silly. The stretched 'muuuuuu' style plays on the familiar cow sound everyone knows from childhood, pushing it just past normal length so it becomes funny instead of realistic. Creators keep it in rotation because it is instantly recognisable, family-friendly, and easy to drop into almost any joke.