the.com/humming
Singing for people who forgot the words but never the tune.
means Producing a low, continuous musical sound with closed lips, or making a steady droning noise.
from From Middle English hummen, a word built to sound like the thing itself — pure onomatopoeia, buzzing since the 1300s.
Mouth shutThe only song requiring no open lips.
Bees tooSame word covers insects, engines, and busy crowds.
Forgotten lyricsHumming often replaces words the brain misplaced.