Dr. Mohammad?

Volume 4, Book 54, Number 537:
Narrated Abu Huraira:
The Prophet said "If a house fly falls in the drink of anyone of you, he should dip it (in the drink), for one of its wings has a disease and the other has the cure for the disease."
1) Where did Mohammad learn about diseases?
2) Did Mohammad learn this at the Kabba?
3) If you dip the fly in the drink, how will you know that the wing with the cure will save you as opposed to the wing with the disease?
4) If a fly falls on your food, should you smear your food with both wings?
5) Is Mohammad a licensed practitioner?