put on one's thinking cap vs ruminate

put on one's thinking cap

ruminate

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. 

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

How often have the words put on one's thinking cap and ruminate occurred in a corpus of books? (source: Google Ngram Viewer )