beetle-crusher vs moon boot

beetle-crusher

moon boot

noun
  • A large hard plastic covering, used to protect a broken foot or ankle while it heals. 

  • A type of footwear made popular in the 1970s, with a thin rubber outsole and no distinct left or right feet. 

How often have the words beetle-crusher and moon boot occurred in a corpus of books? (source: Google Ngram Viewer )