hassle vs knock on wood

hassle

verb
  • To trouble, to bother, to annoy. 

  • To engage in a mock dogfight. 

  • To pick a fight or start an argument with. 

noun
  • Trouble, bother, unwanted annoyances or problems. 

  • A fight or argument. 

  • An action which is not worth the difficulty involved. 

adj
  • hassling; hasslesome 

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 hassle and knock on wood occurred in a corpus of books? (source: Google Ngram Viewer )