introspection vs rumination

introspection

noun
  • A looking inward; specifically, the act or process of self-examination, or inspection of one's own thoughts and feelings; the cognition which the mind has of its own acts and states 

rumination

noun
  • Deep thought or consideration. 

  • The act of ruminating; i.e. chewing cud. 

  • Negative cyclic thinking; persistent and recurrent worrying or brooding. 

  • An eating disorder characterized by repetitive regurgitation of small amounts of food from the stomach. 

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