BOB vs vulva

BOB

noun
  • Vibrator (device designed to stimulate a woman's genitals). 

adj
  • Back-of-the-book; denoting those stamps in a catalogue that are not used for the payment of regular postage fees, and are displayed separately in the catalogue after that listing; the division between these two groups varies with the publisher. 

vulva

noun
  • The external female sexual organs, collectively. 

  • A protrusion on the side of a nematode. 

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