Natto is fermented soy beans, it's commonly eaten for breakfast in Japan. The smell is awful almost as bad as it tastes. It smells like an old sock and tastes exactly what I imagine an old sick tastes like.

I was staying with a Japanese family on a school trip and they offered some to me, not wanting to be impolite I ate it. When they asked me what I thought, I said I liked it. Again only being polite.

Unfortunately for me they took me at my word and gave it to me every day after that. Luckily it was only a few days.