kick a dog when it's down vs rub salt in the wound

kick a dog when it's down

verb
  • To make things worse for someone in an adverse situation. 

rub salt in the wound

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

How often have the words kick a dog when it's down and rub salt in the wound occurred in a corpus of books? (source: Google Ngram Viewer )