User blog comment:FairyRaven/Fairy Tail Chapter 372: Breach, Review and Commentary/@comment-3424593-20140221122115/@comment-7418318-20140221140555

@FTGM: Maybe she doesn't even have a spine. With her not being Human, they might have a completely different anatomy on the inside and just appear similar on the outside.

@all: Maybe Cube is much softer than it looks and that's why the build a stone castle on top of it, instead of burrowing into Cube itself.

Though it's still impressive that Kyouka's body was smashed through the dungeon's stone floor without being pierced.