hunting knife vs tear gas

hunting knife

noun
  • A large knife designed for use in hunting animals, usually with a smooth front edge and a back edge that is partially serrated for sawing. 

tear gas

verb
  • To use tear gas. 

noun
  • Any lachrymatory, non-lethal chemical compound that causes the eyes to sting and water and/or irritates the respiratory system, mostly used for controlling crowds during riots or as self-defense. 

How often have the words hunting knife and tear gas occurred in a corpus of books? (source: Google Ngram Viewer )