entail vs knock on wood

entail

verb
  • To imply, require, or invoke. 

  • To settle or fix inalienably on a person or thing, or on a person and his descendants or a certain line of descendants; -- said especially of an estate; to bestow as a heritage. 

noun
  • That which is entailed. 

  • An estate in fee entailed, or limited in descent to a particular class of issue. 

  • The rule by which the descent is fixed. 

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