rack one’s brains vs ruminate

rack one’s brains

ruminate

adj
  • Having a hard albumen penetrated by irregular channels filled with softer matter, as the nutmeg and the seeds of the North American papaw. 

verb
  • To meditate or reflect. 

  • To meditate or ponder over; to muse on. 

  • To chew cud. (Said of ruminants.) Involves regurgitating partially digested food from the rumen. 

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