ferule vs pepper spray

ferule

verb
  • To punish with a ferule. 

noun
  • A ruler-shaped instrument, generally used to slap naughty children on the hand. 

pepper spray

verb
  • To douse (someone or something) with pepper spray. 

noun
  • A non-lethal chemical agent derived from peppers used in riot control and personal self-defense. 

How often have the words ferule and pepper spray occurred in a corpus of books? (source: Google Ngram Viewer )