Answer:
Once you know it exists, it no longer exists. What is it?
What is often returned, but never borrowed?
This type of food, which is a fungus, is often served on supreme pizza, in spaghetti and in a particular "cream of" style soup
We are two brothers on opposite sides of the road, but we never see each other. Who are we?
Built of metal or wood to divide. It will make us good neighbors, if you stay on your side. What is 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.