keep on at vs prod

keep on at

prod

verb
  • To encourage, to prompt. 

  • To prick with a goad. 

  • To poke, to push, to touch. 

noun
  • A production; a created work. 

  • A light kind of crossbow; a prodd. 

  • A prick or stab with such a pointed instrument. 

  • A poke. 

  • A device (now often electrical) used to goad livestock into moving. 

How often have the words keep on at and prod occurred in a corpus of books? (source: Google Ngram Viewer )