imply vs knock on wood

imply

verb
  • to hint; to insinuate; to suggest tacitly and avoid a direct statement 

  • to suggest by logical inference 

  • to have as a necessary consequence 

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