pencil in vs rub out

pencil in

verb
  • to provisionally schedule 

  • to fill in or write in using pencil 

rub out

verb
  • To delete or erase or remove (something) by rubbing. 

  • To kill, especially to murder. 

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