Seems to be a lot of horse dung involved.
Same reason why most 'magic potions' include hard to achieve steps (steal church parchments, estract the liver of a dog, etc.).
How are these "hard to achieve"?
This is one big benefit of having a dog.
You get to eat its poop?
Apart from parasites and bacteria shit could be beneficial in theory - as its full of minerals and could help to regenerate skin etc.