come clean vs open one's mouth

come clean

verb

  • To confess; admit the truth. 

  • 1921, B. M. Bower, chapter 6, in Sawtooth Ranch 

  • 1977 Oct. 23, John Gardner, "The World Of Tolkien," New York Times (retrieved 12 Sept 2013) 

  • 2005 August 8, "Quotes of the Day," Time (retrieved 12 Sept 2013) 

open one's mouth

verb

  • to speak 

How often have the words come clean and open one's mouth occurred in a corpus of books? (source: Google Ngram Viewer )