mammal vs viper

mammal

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

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

viper

noun
  • A venomous snake in the family Viperidae. 

  • A dangerous, treacherous, or malignant person. 

  • A person who smokes marijuana. 

  • Any venomous snake. 

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