Answer:
Sally, Lisa, and Bernadette are triplets. But Sally and Lisa share something that Bernandette does not. What is it?
What is so delicate that even mentioning it breaks it?
What never gets any wetter no matter how hard it rains?
The day is their night and the night is their day, when I shout and they shout back I run away.
A beautiful succession of sounds.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.