Answer:
What instrument can you hear but never see?
In many hallways you would stand, if not with this in hand.
What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?
They are two brothers. However much they run, they do not reach each other.
A person who chews the ends of their fingers
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.