foment vs touch off

foment

verb
  • To incite or cause troublesome acts; to encourage; to instigate. 

  • To apply a poultice to; to bathe with a cloth or sponge. 

noun
  • Fomentation. 

touch off

verb
  • To start; to cause, especially used for unstable situations that may magnify if disturbed. 

How often have the words foment and touch off occurred in a corpus of books? (source: Google Ngram Viewer )