middle leg vs propagator

middle leg

noun
  • The penis. 

propagator

noun
  • A person who propagates plants 

  • A covered, sometimes heated container for germinating seeds or raising seedlings 

  • A function that represents the quantum propagation of a subatomic particle 

  • A person who disseminates news or rumour 

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