jungle telegraph vs rumor mill

jungle telegraph

noun
  • A gossip network; an informal communication system within a group or organization. 

  • A system used by primitive cultures in remote tropical regions for communication over long distances, such as drum sounds or a relay of runners. 

rumor mill

noun
  • A process in which a group or network of persons originate or promulgate gossip and other unsubstantiated claims. 

How often have the words jungle telegraph and rumor mill occurred in a corpus of books? (source: Google Ngram Viewer )