Answer:
If you have me you want to share me. If you share me you don't have me. What am I?
I move without wings Between silken string I leave as you find My substance behind.
My teeth are sharp my back is straight to cut things up it is my fate.
What has keys but no locks a space but no room and you can enter but can't go in?
I am asleep when you are awake I am awake when you fall asleep. I can fly but no feathers to aid my flight.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.