When I was young – too many years ago – my dad was a coal miner. There are many dangers inherent to working underneath 1000 feet of dirt. One of those dangers is trapped gas that is very difficult to detect and can be deadly. In the old days, coal miners used to bring canaries underground with them. Canaries are quite sensitive to their surroundings. They served as an early warning sign that dangerous gas was present. If the canary died, then the miners had to get out – fast! The miners had to keep an eye on the bird. They also had to listen.