dog-ear vs double over

dog-ear

verb
  • To fold (the corner of the page of a book or other publication). 

noun
  • The folded corner of the page of a book or other publication, either due to having been read many times or intentionally as a sort of bookmark. 

double over

verb
  • To bend over at the waist. 

How often have the words dog-ear and double over occurred in a corpus of books? (source: Google Ngram Viewer )