Answer:
There is one in every corner and two in every room.
A father's child, a mother's child, yet no one's son
In birth I spring forth, in life I unfold. In death I wilt and die, but rebirth restores all.
What is the end of everything?
What has no hands but might knock on your door, and if it does you better open up?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?