Слово brittle имеет два значения. Учим дальше.

Page200. Saints…

'Christ, John, we've only just got started.' Clarke's voice was brittle (unkind and unpleasant).

Page376. Saints…

  'How did I know I'd be seeing you again?' Traynor's mouth seemed parched (dried out because of too much heat), his voice brittle (delicate and easy broken).