Penguins have a distinct mating call for each other. They mate for life, and even when they’ve been separated by months and miles of freezing tundra, when they hear the call of their beloved, they recognize that song right away.
The same thing happened to me when I had my son.
Twenty-three years ago today, they handed my baby to me and I studied every fingernail and toe. He was absolutely beautiful; a perfect creation that I couldn't believe was mine. We bonded briefly, then they wheeled him away to clean him up and finished tending to me as well.
I was taken to my hospital room and got settled in. Then, down the hallway in the distance, I heard a baby's cry. My ears perked up. My heartbeat raced. My milk flowed. That was my baby. I just knew it. Somehow, though we'd only spent a few minutes together so far, I knew he was mine. I knew his cry.