Answer:
Deep, deep, do they go. Spreading out as they go. Never needing any air. They are sometimes as fine as hair.
I work when I play and play when I work
I am the only thing that place today before yesterday. (one word)
I have a lot to say but can't be heard because I can't speak one single word. What am I?
I can run but not walk. Wherever I go thought follows close behind.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?