Answer:
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
How can you burn an apple, blueberry, rose and pumpkin without leaving any ashes but retaining the smell of it?
I turn around once. What is out will not get in. I turn around again. What is in will not get out.
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.
Sharp and long, flag of the world. What is it?
I have two eyes in the front and a lot of eyes on my tail