Answer:
They come out at night without being called. They are lost in the day without being stolen. What are they?
You see a boat filled with people. It has not sunk but when you look again you don't see a single person on the boat. Why?
I can be repeated but rarely in the same way. I can't be changed but can be rewritten. I can be passed down but should not be forgotten.
I'm not a bird but I can fly through the sky. I'm not a river but I'm full of water.
I am perfect with a head perfect without a head; Perfect with a tail perfect without a tail; Perfect with either neither or both.
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.