mammal vs wild horse

mammal

noun
  • An animal of the class Mammalia, characterized by being warm-blooded, having hair and producing milk with which to feed its young. 

  • A vertebrate with three bones in the inner ear and one in the jaw. 

wild horse

noun
  • A member of the species Equus ferus, sometimes excluding the domesticated horse. 

  • A feral horse. 

  • An untamed horse. 

How often have the words mammal and wild horse occurred in a corpus of books? (source: Google Ngram Viewer )