knock on wood vs suspicion

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. 

suspicion

verb
  • To suspect; to have suspicions. 

noun
  • Uncertainty, doubt. 

  • The imagining of something without evidence. 

  • The act of suspecting something or someone, especially of something wrong. 

  • A trace, or slight indication. 

  • The condition of being suspected. 

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