The newborn smile. It happens during most newborn photography sessions but not always at the right moment (newborns don't always listen to direction ;)).
This newborn smiled a few times during her session when she was warm, comfortable and when she heard her beautiful Mama's voice. I know baby books say "official smiles" happen around six weeks and that the "smiles" you see before are reflexes or gas.
But smiling when you hear your Mama's voice? That has to be real.