Morgan's mule vs horseflesh

Morgan's mule

noun
  • The horse (instrument of punishment). 

horseflesh

noun
  • Horses collectively, with reference to driving, riding, or racing. 

  • A species of Bahama mahogany, Lysiloma sabicu and Lysiloma latisiliquum. 

  • The flesh of a horse; horsemeat. 

adj
  • Of the colour of horseflesh; of a peculiar reddish-brown hue. 

How often have the words Morgan's mule and horseflesh occurred in a corpus of books? (source: Google Ngram Viewer )