bite off vs get blood out of a stone

bite off

verb
  • To accept or commit oneself to a task, project, notion, or responsibility, especially one which presents challenges. 

  • To bite so hard as to remove something from its source. 

  • To acquire, especially in an abrupt or forceful manner. 

get blood out of a stone

verb
  • To do something difficult, frustrating, or pointless. 

How often have the words bite off and get blood out of a stone occurred in a corpus of books? (source: Google Ngram Viewer )