crack up vs falsetto

crack up

verb
  • To cry up; to extol. 

  • To cause to laugh heartily. 

  • To become insane; to suffer a mental breakdown. 

  • To crash an aircraft or automobile. 

  • To laugh heartily. 

adj
  • Funny; hilarious 

falsetto

verb
  • To sing or utter in falsetto. 

noun
  • A person who sings in falsetto. 

  • The "false" (singing) voice in any human, usually airy and lacking a purity of vowels; created by utilizing the next highest vocal folds above those used for speech and normal range singing. It is commonly confused with the head voice register. 

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