Answer:
What binds two people yet touches only one?
What goes around and around the wood, but never goes into the wood?
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
Die without me, never thank me. Walk right through me, never feel me. Always watching, never speaking. Always lurking, never seen.
People are hired to get rid of me. I'm often hiding under your bed. In time I'll always return you see. Bite me and you're surely dead.
What do angels sing in the shower?