Answer:
Once you know it exists, it no longer exists. What is it?
It is in every mountain, it's not in any hill, it's not in all the world, and yet it's in the mill.
What word in the dictionary is weird?
Never ahead, ever behind, yet flying swiftly pastΝΎ For a child I last forever, for adults I'm gone too fast.
People want it, and when they have it, they use it by giving it
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.