I didn't know what hollow forms were until I encountered them in woodturning. Luckily, they are not the evil type--as in the manga, just simply innocuous, hollow wooden objects. But that doesn't mean they are free of danger.
"Hollow form" is an interesting term, often referring to a hollow vessel with a very small opening, relative to the size of the object. It is advanced turning that requires special hollowing tools. The danger comes when I try to hog out the inside of the piece. It's hard to judge the vessel's thickness through that small opening, so hollowing is a series of blind cuts. One cut too deep and the thing blows up! I would end up with two halves instead of one whole. It is very sad when that happens... Yes, there are laser guided apparatus for hollowing, but these systems tend to be too large for a mini lathe.
Of course, hollow forms, with their challenges, are often used to demonstrate and gauge the skill of a woodturner: the thinner the wall, the deeper the form, the smaller the opening, the better.
As I turned hollow form, it occurred to me that this was the most folly and vain of all woodturning activities. Here I am, transforming a piece of useful timber into a useless fragile vessel, with an opening too small to fit anything in. By throwing away 90% of the useful material, I locked that piece of wood into this 3D form, preventing any future reuse or re-purpose. But then, that's just the rational, practical half of my brain speaking; the other half knows that when an object just sits on it's bottom, looking pretty, good for nothing, it's "ART".