bath mat vs sheepskin

bath mat

noun
  • A small mat used next to a bathtub to absorb water and thus prevent slipping. 

sheepskin

noun
  • A diploma. 

  • The tanned skin of a sheep with the fleece left on, especially when used for clothing, rugs, etc. 

  • The skin of a sheep, especially when used to make parchment or in bookbinding. 

How often have the words bath mat and sheepskin occurred in a corpus of books? (source: Google Ngram Viewer )