dirty protest vs sit-in

dirty protest

noun
  • A form of protest where a prisoner refuses to use the toilet and instead defecates and urinates within his or her cell. 

sit-in

noun
  • A peaceful form of protest in which people occupy an area and refuse to leave. 

adj
  • Designed to be sat in. 

How often have the words dirty protest and sit-in occurred in a corpus of books? (source: Google Ngram Viewer )