HORSE vs shithead

HORSE

noun
  • A poker variant consisting of five different poker variants, with the rules changing from one variant to the next after every hand. 

shithead

noun
  • A card game, the aim of which is to lose one's cards. 

  • A stupid or contemptible person. 

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