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This is when you know the words to a song , but your somewhere in which you can not sing the words outloud , such as a classroom, so you use a low mumble voice to portray the words and hum from the back of your throat as if you were making the beat. In all reality your the only one who even has a clue what you are singing.
The kid behind me must have a song stuck in his head, he keeps mumble humming something I can't understand .

Hunter from Spanish class is a professional Mumble Hummer , I can never understand what he is singing even when he is trying.
by morningcartoons January 08, 2010
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