Simple past tense and past participle of mum.(verb)
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Use "mummed" in a sentence
"To this the other, Billi with the Boule, who had mummed and mauled up to that (for he was hesitency carried to excelcism) rather amusedly replied: Woowoo would you be grossly surprised, Hill, to learn that, as it so happens, I honestly have not such a thing as the loo, as the least chance of"
"He saw the rags rise higher and higher above him until at last they tumbled upon the floor from the body of a naked man -- a thin, a bony, a hideous caricature of man, that mouthed and mummed and, wabbling upon its weak and shaking legs, crumpled to the floor again, still laughing -- laughing horribly."