Although the sight of Fusou eating with grace is fine, I must ask: how the hell does a sweet potato go ballistic when roasting?
When the universe is out to screw you over. Seriously though, I think that is just a random spark hit her forehead and started smoking. Then again, I'm not sure how does that happen...
I always notch mine when I roast them, but man, imagine hot chestnut smacking you in the face. It's especially worse when you get hit by the hot flesh as well, not just the shell.