Because humans have five senses: feel, see, taste, hear, and smell. When you step on a nail you basically going to feel it and you brain can sense that and it can trigger nerves which can cause pain.
The skin IS considered a organ as it is apart of the integementry system. And it is the largest organ in the body. The skin has a epidermal layer, a dermal layer, fatty tissue, and several other associated factors.
Food poisoning is not a type of food borne disease.
