Answer:
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
Two people are born at the same moment, but they don't have the same birthdays. How could this be?
Who is that with a neck and no head, two arms and no hands? What is it?
It is worldwide, but once only a spider could weave one
Mountains will crumble and temples will fall. And no man can survive its endless call.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?