barbed wire vs picket fence

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. 

picket fence

noun
  • A simple fence made from wooden pickets, connected by horizontal bars. 

  • A series of spaced perpendicular striations that occasionally occur in aurorae. 

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