It's so bad because they have to use an animal that's healthy to make sure they get the right results and (obsiously) they have to kill the animal.
It is because you can get ink poisoned if you keep it on you too long
he could make a potion that does bad stuff
They don't have a noticable odor, but you'll see soft spots, bruises, or spots of mold so it will be obvious.
yes it is because sometimes when you think about bad things your actions follow. your brain is connected to your nerves so when you think you react.