trauma vs warning bell

trauma

noun
  • An event that causes great distress. 

  • An emotional wound leading to psychological injury. 

  • Any serious injury to the body, often resulting from violence or an accident. 

warning bell

noun
  • A problematic or alarming aspect. 

  • A bell rung to warn people of a danger. 

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