gibber vs mussitate

gibber

verb
  • To jabber, talk rapidly and unintelligibly or incoherently. 

noun
  • Gibberish, unintelligible speech. 

  • A balky horse. 

  • A stone or rock, of chalcedony or similar mineral, found strewn over arid regions of inland Australia; a gibber stone. 

mussitate

verb
  • To talk indistinctly; to mutter. 

  • To say (words, etc.) indistinctly; to mutter. 

How often have the words gibber and mussitate occurred in a corpus of books? (source: Google Ngram Viewer )