agitate vs tremble

agitate

verb
  • To cause to move with a violent, irregular action; to shake. 

  • To disturb or excite; to perturb or stir up (a person). 

tremble

verb
  • To shake, quiver, or vibrate. 

  • To fear; to be afraid. 

noun
  • A shake, quiver, or vibration. 

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