infer vs knock on wood

infer

verb
  • To lead to (something) as a consequence; to imply. 

  • To introduce (something) as a reasoned conclusion; to conclude by reasoning or deduction, as from premises or evidence. 

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