dumber than a rock vs hatstand

dumber than a rock

adj
  • Extremely stupid. 

hatstand

adj
  • Crazy, insane. 

noun
  • A device used to store hats upon, consisting of a vertical pole with a sturdy base to prevent toppling, and an array of pegs to hold the hats. 

How often have the words dumber than a rock and hatstand occurred in a corpus of books? (source: Google Ngram Viewer )