kill by hanging vs mow down

kill by hanging

verb
  • to kill someone by suspending them by the neck 

mow down

verb
  • To kill or slaughter, or to injure by knocking down, especially in large numbers and in a ruthless manner. 

  • To cut down, especially in large numbers. 

How often have the words kill by hanging and mow down occurred in a corpus of books? (source: Google Ngram Viewer )