face down vs prone

face down

verb
  • To confront; to abash by stern looks. 

prone

verb
  • To place in a prone position, to place face down. 

adj
  • Of the hand, forearm or foot: turned facing away from the body; with the thumb inward or big toe downward. 

  • Having a downward inclination or slope. 

  • Lying face downward. 

  • Predisposed, liable, inclined. 

How often have the words face down and prone occurred in a corpus of books? (source: Google Ngram Viewer )