Humming quietly to yourself is a self confirming sound.
This is a sidetrack from the central theme of the essay, because it's not a necessity for survival, and only a few animals do anything like this. I believe cats do something similar when they purr, frogs when they croak, and hens and camels can make similar sounds.
The possibility comes naturally with our human body, and our human vocal chords. I find it is ritualised by Buddhist monks when droning their texts. This is far simpler. There is no text!
I find humming quietly to myself a useful way of keeping peace with myself, particularly when everything outside is too noisy, busy and overpowering, like when walking through a crowd of bustling people. And it's somehow sensible, because at these times i'm not interested in scenting and my mouth is closed.
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