Natto are fermented soy beans. They are essentially half decomposed by bacteria! They are coated with a slippery, cheesy, stringy sauce. They don't smell very good at first whiff. But they are an acquired taste, so if you keep trying them, you, too, will eventually grow to love natto. I know a person who loves them so much, he maintains a natto stash in his freezer! This natto is from Ichibei, and it comes with tuna, which is a very nice combination.
Francis
Mixing with yogurt completely removes the natto taste and smell. Not good if you like natto, but given that natto is very healthy to consume, it would make it palatable for those that don't (like natto).