barbed wire vs razor wire

barbed wire

noun
  • Twisted strands of steel wire, often coated with zinc, having barbs evenly spaced along them; used to construct agricultural and military fences. 

razor wire

noun
  • A form of securing wire similar to barbed wire, but with a series of short blades instead of barbs. Also, a length thereof. 

How often have the words barbed wire and razor wire occurred in a corpus of books? (source: Google Ngram Viewer )