cherish vs knock on wood

cherish

verb
  • To have a deep appreciation of; to hold dear. 

  • To treat with affection, care, and tenderness; to nurture or protect with care. 

knock on wood

verb
  • To take a customary action to ward off some misfortune that is believed to be attracted by a presumptuous statement. 

intj
  • Hopefully; a self-directive to undertake the customary action to ward off bad luck. 

How often have the words cherish and knock on wood occurred in a corpus of books? (source: Google Ngram Viewer )