plunk vs plunk down

plunk

noun
  • The dull thud of something landing on a surface. 

verb
  • To pluck and quickly release (a musical string). 

  • To be a truant from (school). 

  • To intentionally hit the batter with a pitch. 

  • To croak. 

  • To land suddenly or heavily; to plump down. 

  • To drop or throw something heavily onto or into something else, so that it makes a dull sound. 

plunk down

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