cop out vs slip out

cop out

verb
  • To avoid or shirk, either by failing to perform, or by performing in a grossly insufficient, negligent, or superficial manner. 

  • To plead guilty and ask for mercy. 

slip out

verb
  • To be said or revealed by accident. 

  • To leave quietly, and unnoticed. 

  • To go out for a brief moment; pop out 

How often have the words cop out and slip out occurred in a corpus of books? (source: Google Ngram Viewer )