leave alone vs slip in

leave alone

verb
  • To desist or refrain from involvement with. 

  • To stop bothering (a person). 

slip in

verb
  • To include (e.g. a certain word or phrase) into a sentence discreetly 

  • To enter discreetly 

  • To play a subtle pass into someone in a goalscoring position. 

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