perturb vs tug at someone's heartstrings

perturb

verb
  • To disturb; to bother or unsettle. 

  • To modify the motion of a body by exerting a gravitational force. 

  • To modify slightly, such as an equation or value. 

  • To slightly modify the motion of an object. 

tug at someone's heartstrings

How often have the words perturb and tug at someone's heartstrings occurred in a corpus of books? (source: Google Ngram Viewer )