Answer:
When I live I cry, If you don't kill me I'll die.
You use it between your head and your toes, the more it works the thinner it grows.
My teeth are sharp, my back is straight, to cut things up it is my fate.
Describes universities like Harvard and can be poisonous.
What loses its head in the morning and gets it back at night?
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.