The sound of toenails clicking across the kitchen floor, the thump of a tail responding to your voice in the dark, the jingling of tags on a collar--all are sounds welcomed by every dog lover. Just as we have grown fond of the antics and traits of our beloved pets, our dogs have grown accustomed to the sound of our keys unlocking the door, our hands reaching into a jar for a doggie treat, and our sharing a spot on the couch. This mutual, unconditional...