knock on wood vs know

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. 

know

verb
  • To perceive the truth or factuality of; to be certain of or that. 

  • To experience. 

  • To understand or have a grasp of through experience or study. 

  • To be or become aware or cognizant. 

  • To be able to play or perform (a song or other piece of music). 

  • To be acquainted or familiar with; to have encountered. 

  • To be aware of; to be cognizant of. 

  • To recognize as the same (as someone or something previously encountered) after an absence or change. 

  • To have knowledge; to have information, be informed. 

noun
  • Knowledge; the state of knowing. 

  • Knowledge; the state of knowing; now confined to the fixed phrase ‘in the know’ 

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