erogenous zone vs penis

erogenous zone

noun
  • A part of the human body that is particularly responsive to sexual stimulation. 

penis

noun
  • The male reproductive organ used for sexual intercourse that in the human male and some other mammals is also used for urination; the tubular portion of the male genitalia (excluding the scrotum). 

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