Pets...miners used to take canaries with them into mines as poison gas detectors. If the birds became sick or died while in the mines, the miners knew that poison gas was present, and escaped unharmed. Thus, the canary became the first poison gas (CO) detector. Birds breathe faster than man and have faster metabolic rates thus show effects earlier than we do. If a pet suddenly becomes ill or dies, think of the possibility of a toxic exposure and have the house checked.