devil's doorbell vs nub

devil's doorbell

noun
  • The clitoris. 

nub

noun
  • The clitoris. 

  • a pointing stick 

  • A small lump or knob. 

  • The essence or core of an issue, argument etc. 

verb
  • To push; to nudge. 

  • To beckon. 

  • To hit the ball weakly. 

How often have the words devil's doorbell and nub occurred in a corpus of books? (source: Google Ngram Viewer )