churr vs sough

churr

verb
  • To make the low vocal sound of some birds. 

noun
  • A low vocal sound made by some birds. 

sough

verb
  • To make a soft rustling or murmuring sound. 

  • To drain. 

noun
  • A gentle breeze; a waft; a breath. 

  • A murmuring sound; rushing, rustling, or whistling sound. 

  • A (deep) sigh. 

  • A small drain; an adit. 

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