let cat out of the bag vs uncover

let cat out of the bag

uncover

verb
  • To remove one's hat or cap as a mark of respect. 

  • To reveal the identity of. 

  • To expose the genitalia. 

  • To remove a cover from. 

  • To show openly; to disclose; to reveal. 

  • To expose (lines of formation of troops) successively by the wheeling to right or left of the lines in front. 

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