knock on wood vs mistrust

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. 

mistrust

verb
  • To suspect, to imagine or suppose (something) to be the case. 

  • To be suspicious. 

  • To have no confidence in (something or someone). 

  • To be wary, suspicious or doubtful of (something or someone). 

noun
  • Lack of trust or confidence; distrust, untrust. 

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