“Blood Quill” What?!

In the language of Harry Potter, Blood Quill means…

The ‘Blood Quill is used by Dolores Umbridge throughout Harry Potter and the Order of the Phoenix to carry out her perverse punishment of “cutting up” students. In the fifth book, Harry has detention with Professor Umbridge on several occasions. During these detentions, he is required to write lines (I must not tell lies), and is not released from this until Umbridge believes “the message has sunk in.” Rather than using a regular quill, Umbridge makes Harry use a blood quill, which is described as unusually sharp with a black nib. As the user writes, the quill magically (and painfully) cuts into the back of the user’s hand and uses their blood for ink. When carried out repeatedly over a period, this can lead to permanent scarring, as shown by Harry to Rufus Scrimgeour in Harry Potter and the Half-Blood Prince and Harry Potter and the Deathly Hallows.

Other victims of this form of detention include Lee Jordan. In the film interpretation, all members of Dumbledore’s Army were punished using this method. In fandom, most people refer to this as a “Blood Quill.”^{[citation needed]} Presumably, the inspiration for this is Kafka’s “In the Penal Colony“.

That explains it.

http://en.wikipedia.org/wiki/Magical_objects_in_Harry_Potter#Blood_Quill