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A noise made by breathing out through your nose whilst gently tapping the top of your mouth with your tongue.

Typically performed when bored.
Mate 1: Ah this is boring....hey what is that noise?!
Mate 2: <cough> sorry. I was just humadruming
Mate 1: Geeez I thought you were dying. My gran sounded like that when she Took The Top Escalator
by digital.sam September 28, 2009