The word Mutered is misspelled against Muttered, which is past tense of "Mutter"
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Muttered has double "tt" is mispronounced as "t"
Remember double 'TT' in between the strings mu & ered which should not be misspelled with single 'T'
Wrong Spelling: mu-t-ered
Correct Spelling: mu-tt-ered
Check more misspelled words of Muttered to spell it correct.