mushroom tip vs skull

mushroom tip

noun
  • The glans penis. 

skull

noun
  • The mind or brain. 

  • A crust formed on the ladle, etc. by the partial cooling of molten metal. 

  • The crown of the headpiece in armour. 

  • A shallow bow-handled basket. 

  • The main bones of the head considered as a unit; including the cranium, facial bones, and mandible. 

  • These bones as a symbol for death; death's-head. 

verb
  • To strike the top of (the ball). 

  • To hit in the head with a fist, a weapon, or a thrown object. 

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