look back vs send back

look back

verb
  • To think of (past events) in retrospect. 

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

  • To reconsider or regret. 

send back

verb
  • To remind (someone) of a previous time in the past. 

  • To return (something) to its origin. 

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