Answer:
What is something you will never see again?
One might hang a locket from this
I look at you, you look at me, I raise my right, you raise your left
What instrument plays from the heart?
You fill it and it empties, A metaphor for plenty, Depending on what half you see, It's either full or empty
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.