cower vs pull back

cower

verb
  • To crouch or cringe, or to avoid or shy away from something, in fear. 

  • To cause to cower; to frighten into submission. 

pull back

verb
  • Used other than figuratively or idiomatically: see pull, back. 

  • To retreat. 

  • To pass (the ball) into a position further from the attacking goal line. 

  • To score when the team is losing. 

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