BOB vs gonad

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. 

gonad

noun
  • A sex organ that produces gametes; specifically, a testicle or ovary. 

  • A testicle. 

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