let cat out of the bag vs unveil

let cat out of the bag

unveil

verb
  • To remove a veil; to reveal oneself. 

  • to show, especially for the first time 

  • To remove a veil from; to uncover; to reveal something hidden. 

How often have the words let cat out of the bag and unveil occurred in a corpus of books? (source: Google Ngram Viewer )