Answer:
There are millions of me. I am very small but when moving fast I am deadly.
Give it food and it will live, give it water and it will die.
You use it between your head and your toes, the more it works the thinner it grows.
All about, but cannot be seen, Can be captured, cannot be held, No throat, but can be heard. Who am I?
What is full of holes but still holds water
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?