block heater vs cauldron

block heater

noun
  • An electric heater that heats the engine of a car to ease starting in cold weather. 

cauldron

noun
  • A large bowl-shaped pot used for boiling over an open flame. 

  • A strategic encirclement. 

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