A dog can be a person’s best friend， or so the theory goes. But that relationship can be tested when a dog begins barking at an empty corner of a room， at a door， or anywhere where there doesn’t appear to be any activity at all taking place. Is the dog hallucinating?理论上，狗可能是在对某种声音作出反应，可能是远处车辆的鸣笛声，而狗身边的人听不到这个声音。
