Answer:
There are several different kinds, but the one you pick doesn't do its job. What is it?
I am a fire's best friend. When fat, my body fills with wind. When pushed to thin, through my nose I blow. Then you can watch the embers glow.
Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble.
I can travel from there to here by disappearing, and here to there by reappearing.
In marble halls as white as milk, lined with a skin as soft as silk. Within a fountain crystal-clear. A golden apple doth appear. No doors there are to this stronghold, yet thieves break in and steal the gold.
What did the piece of wood say when he saw the screwdriver and screws approaching?