knock for a loop vs nonplus

knock for a loop

verb
  • To astonish; to stagger or overwhelm; to confuse or disorient. 

nonplus

verb
  • To bewilder or perplex (someone); to confound, to flummox. 

noun
  • A state of bewilderment or perplexity. 

How often have the words knock for a loop and nonplus occurred in a corpus of books? (source: Google Ngram Viewer )