expose vs let cat out of the bag

expose

verb
  • To submit to an active (mostly dangerous) substance like an allergen, ozone, nicotine, solvent, or to any other stress, in order to test the reaction, resistance, etc. 

  • To make available to other parts of a program, or to other programs. 

  • To abandon, especially an unwanted baby in the wilderness. 

  • To reveal, uncover, make visible, bring to light, introduce (to). 

  • To subject photographic film to light thereby recording an image. 

let cat out of the bag

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