boil up vs flare up

boil up

verb
  • To become more excited, intense or exciting. 

  • To cook or prepare by boiling. 

noun
  • A traditionally Maori soup/stew made with potatoes, pork and other ingredients. 

flare up

verb
  • To become more intense suddenly. 

  • To burst out suddenly, as in anger. 

  • To burn brightly again. 

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