human chain vs lie-in

human chain

noun
  • A form of demonstration in which people link their arms as a show of political solidarity. 

  • A bucket brigade. 

lie-in

noun
  • A form of protest where a group of people lie down in a public area. 

  • A period spent lying in bed for longer than usual after one has woken up. 

How often have the words human chain and lie-in occurred in a corpus of books? (source: Google Ngram Viewer )