flay vs gnaw away at

flay

verb
  • To cause to fly; put to flight; drive off (by frightening). 

  • To frighten; scare; terrify. 

  • To be fear-stricken. 

  • To strip the skin off; to skin. 

  • To lash or whip. 

noun
  • A fright; a scare. 

  • Fear; a source of fear; a formidable matter; a fearsome or repellent-looking individual. 

gnaw away at

How often have the words flay and gnaw away at occurred in a corpus of books? (source: Google Ngram Viewer )