head for the hills vs take off

head for the hills

verb
  • To go to a safe place; to seek refuge; to flee. 

  • To travel to a higher elevation, especially to a rural region on vacation. 

take off

verb
  • To depart. 

  • To absent oneself from (work or other responsibility), especially with permission. 

  • To quantify. 

  • To remove. 

  • To leave the ground and begin flight; to ascend into the air. 

  • To imitate, often in a satirical manner. 

  • To become successful, to flourish. 

How often have the words head for the hills and take off occurred in a corpus of books? (source: Google Ngram Viewer )