BOB vs sexual congress

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. 

sexual congress

noun
  • sexual intercourse 

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