pitter-patter vs thump

pitter-patter

noun
  • A soft, percussive sound, as of tiny feet, or of rain on a rooftop. 

thump

noun
  • The sound of such a blow; a thud. 

  • A blow that produces a muffled sound. 

verb
  • To throb with a muffled rhythmic sound. 

  • To hit (someone or something) as if to make a thump. 

  • To cause to make a thumping sound. 

  • To thud or pound. 

How often have the words pitter-patter and thump occurred in a corpus of books? (source: Google Ngram Viewer )