knock on wood vs suspect

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. 

suspect

verb
  • To believe (someone) to be guilty. 

  • To have suspicion. 

  • To imagine or suppose (something) to be true, or to exist, without proof. 

  • To distrust or have doubts about (something or someone). 

noun
  • A person who is suspected of something, in particular of committing a crime. 

adj
  • Viewed with suspicion; suspected. 

  • Viewing with suspicion; suspecting. 

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