forget vs mull over

forget

verb
  • To lose remembrance of. 

  • To unintentionally not do, neglect. 

  • To unintentionally leave something behind. 

  • To cease remembering. 

  • Euphemism for fuck, screw (a mild oath). 

mull over

verb
  • To think deeply about something; to ponder, deliberate or ruminate. 

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