Answer:
The little pink nub that helps rectify mistakes.
What can you never get rid of when you lose it?
Deep, deep, do they go. Spreading out as they go. Never needing any air. They are sometimes as fine as hair
A standard dimension for sandwiches and rulers
Retired people want these to be large and birds want them to hatch.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?