mugger crocodile vs wrong 'un

mugger crocodile

noun
  • A crocodile, Crocodylus palustris 

wrong 'un

noun
  • A googly. 

  • A dishonest or disreputable person; a crook or rogue. 

  • A horse deliberately held back in order to lose a race. 

How often have the words mugger crocodile and wrong 'un occurred in a corpus of books? (source: Google Ngram Viewer )