draw blood vs impair

draw blood

verb
  • To have an injurious effect; to strike home, as a barb or insult. 

  • To wound one's opponent in such a way that they bleed. 

impair

verb
  • To weaken; to affect negatively; to have a diminishing effect on. 

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