behead vs string up

behead

verb
  • To deliberately remove the head of; to cut off (someone's) head. 

string up

verb
  • To kill (a person) by hanging, especially to lynch. 

  • To concatenate; to link in a line. 

  • To suspend by means of rope, cord or similar material. 

How often have the words behead and string up occurred in a corpus of books? (source: Google Ngram Viewer )