balls of steel vs yarbles

balls of steel

noun
  • Courage, audacity. 

yarbles

noun
  • Courage, fortitude, or machismo. 

  • Nonsense; something of unacceptably poor quality. 

  • Information that is false or otherwise misleading. 

  • Testicles. 

intj
  • Expressing disgust, annoyance, frustration, or disapproval. 

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