headphone vs stethoscope

headphone

noun
  • A cushioned speaker placed on, over, or inside the ear, normally used in left/right pairs. 

stethoscope

noun
  • A medical instrument used for listening to sounds produced within the body. 

verb
  • To auscultate, or examine, with a stethoscope. 

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