threaten vs tremble

threaten

verb
  • To make a threat against someone; to use threats. 

  • To portend, or give a warning of. 

  • To call into question the validity of (a belief, idea, or viewpoint); to challenge. 

  • He threatened me with a knife. 

  • To menace, or be dangerous. 

  • To be close to equaling or surpassing (a record, etc.) 

tremble

verb
  • To fear; to be afraid. 

  • To shake, quiver, or vibrate. 

noun
  • A shake, quiver, or vibration. 

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