keep one's fingers crossed vs knock on wood

keep one's fingers crossed

verb

  • To hope for the best, to show support. 

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 keep one's fingers crossed and knock on wood occurred in a corpus of books? (source: Google Ngram Viewer )