foreskin vs knit cap

foreskin

noun
  • The nerve-dense, retractable fold of skin which covers and protects the head of the penis in humans and some other animals. 

verb
  • To remove the foreskin. 

  • To sexually stimulate by manipulating the foreskin. 

knit cap

noun
  • A soft, head-hugging cap usually without a specified front or back, barring those with designs or logos 

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