chew over vs contemplate

chew over

verb
  • To think deeply about; to ponder or mull over. 

contemplate

verb
  • To look at on all sides or in all its aspects; to view or consider with continued attention; to regard with deliberate care; to meditate on; to study, ponder, or consider. 

  • To consider as a possibility. 

How often have the words chew over and contemplate occurred in a corpus of books? (source: Google Ngram Viewer )