Pony Express vs dak

Pony Express

name
  • A 19th-century mail service delivering messages across North America by means of riders on horseback. 

dak

noun
  • A post system by means of transport relays of horses stationed at intervals along a route or network, carrying mail and passengers. 

  • A dak bungalow. 

verb
  • To suddenly pull down someone's pants as a prank; to pants. 

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