knock on wood vs suppose

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. 

suppose

verb
  • To theorize or hypothesize. 

  • To require to exist or to be true; to imply by the laws of thought or of nature. 

  • To put by fraud in the place of another. 

  • To take for granted; to conclude, with less than absolute supporting data; to believe. 

  • To imagine; to believe; to receive as true. 

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