flaky vs horse’s tail

flaky

adj
  • Unreliable; working only on an intermittent basis; likely due to malfunction. 

  • Consisting of flakes or of small, loose masses; lying, or cleaving off, in flakes or layers; flakelike. 

  • Unreliable; likely to make plans with others but then abandon those plans. 

horse’s tail

How often have the words flaky and horse’s tail occurred in a corpus of books? (source: Google Ngram Viewer )