joke vs perk up

joke

verb
  • To do or say something for amusement rather than seriously. 

  • To dupe in a friendly manner for amusement; to mess with, play with. 

noun
  • An amusing story. 

  • The root cause or main issue, especially an unexpected one 

  • A laughably worthless thing or person; a sham. 

  • Something that is far easier or far less challenging than expected. 

  • Something said or done for amusement, not in seriousness. 

perk up

verb
  • to become more lively or enthusiastic. 

  • To cause to be more upright, straighten up 

  • to cause to be more lively or enthusiastic. 

  • His ears perked up when he heard there would be ice cream. 

  • To become more upright 

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