pitter-patter vs throb

pitter-patter

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

throb

noun
  • A beating, vibration or palpitation. 

verb
  • To pound or beat rapidly or violently. 

  • To pulse (often painfully) in time with the circulation of blood. 

  • To vibrate or pulsate with a steady rhythm. 

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