Answer:
A device for finding furniture in the dark.
If you have it, you want to share it. If you share it, you don't have it.
What is that you will break everytime you name it?
When the creeper passes, all the grass kneels
My life can be measured in hours, I serve by being devoured. Thin, I am quick. Fat, I am slow. Wind is my foe.
You use it between your head and your toes, the more it works the thinner it grows.