knock back vs wuss out

knock back

verb
  • To reject; to refuse. 

  • To drink an alcoholic beverage swiftly or often. 

  • To stun; to surprise. 

  • To press or knead (dough) so as to remove air bubbles. 

wuss out

verb
  • To fail to do something because of cowardice. 

How often have the words knock back and wuss out occurred in a corpus of books? (source: Google Ngram Viewer )