fluster vs warning bell

fluster

noun
  • A state of being flustered; overwrought confusion. 

verb
  • To confuse; befuddle; throw into panic by making overwrought with confusion. 

  • To be in a heat or bustle; to be agitated and confused. 

warning bell

noun
  • A problematic or alarming aspect. 

  • A bell rung to warn people of a danger. 

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