gibbering vs yapping

gibbering

noun
  • Manic, meaningless speech; babble. 

adj
  • Prone to meaningless vocalization, especially excited and confused utterances, like a beast or monster. 

yapping

noun
  • A sound that yaps, especially the continued barking of a small dog. 

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