convulse vs ferment

convulse

verb
  • To violently shake or agitate. 

  • To suffer violent involuntary contraction of the muscles, producing contortions of the body or limbs. 

  • To create great laughter. 

ferment

verb
  • To stir up, agitate, cause unrest or excitement in. 

  • To react, using fermentation; especially to produce alcohol by aging or by allowing yeast to act on sugars; to brew. 

noun
  • Something, such as a yeast or barm, that causes fermentation. 

  • A gentle internal motion of the constituent parts of a fluid; fermentation. 

  • A state of agitation or of turbulent change. 

  • A catalyst. 

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