rack brains vs reflect

rack brains

reflect

verb
  • To mirror, or show the image of something. 

  • To bend back (light, etc.) from a surface. 

  • To be mirrored. 

  • To agree with; to closely follow. 

  • To be bent back (light, etc.) from a surface. 

  • To give evidence of someone's or something's character etc. 

  • To think seriously; to ponder or consider. 

How often have the words rack brains and reflect occurred in a corpus of books? (source: Google Ngram Viewer )