When my oldest child was born, we were in a hospital room with three other mothers and newborns. I could recognize his cry from the hall outside the room, or the shower from the day after he was born.
I find it fascinating. I can even tell the difference between a 'I'm not getting my own way' cry and a 'I'm hurt' cry. One sends you running; the other just makes you roll your eyes.
Is this something that's in built in mothers?