It's SO aggravating that Hogwarts doesn't even detect, let alone bar Dark Objects. In a world where JKR had some of the most obvious protections on a school, A Teacher used a Blood Quill on a student. I enjoyed this quieter chapter, and its buildup of tension.
Author's response
Now how can the little darlings develop without the staff fully trusting them? You must not be a Pureblood. . . .