fall back vs flump

fall back

verb
  • Used other than figuratively or idiomatically: see fall, back. 

  • To retreat. 

  • To fail to fulfill a promise or purpose. 

flump

verb
  • To move or fall heavily, or with a dull sound. 

  • To drop something heavily or with a dull sound. 

noun
  • A type of large marshmallow. 

  • A fat out-of-shape person. 

  • The dull sound so produced. 

How often have the words fall back and flump occurred in a corpus of books? (source: Google Ngram Viewer )