When my son was about three days old, I was still figuring out breast-feeding—how to do it, where to do it.

One of my worries, though, was our big shaggy Disney dog Guinness and how she would react to the baby. Guinness was my girl. She looked more like me than my own child—same shaggy brown hair, same brown eyes. She was the center of our attention for the eight years we’d had her, so I even stupidly bought a muzzle imagining her unwelcoming reaction to the baby.