heighten vs rub salt in the wound

heighten

verb
  • To make high; to raise higher; to elevate. 

  • To advance, increase, augment, make larger, more intense, stronger etc. 

rub salt in the wound

verb
  • To make an injury, physical or emotional, feel worse. 

How often have the words heighten and rub salt in the wound occurred in a corpus of books? (source: Google Ngram Viewer )