Muggles' Guide to Harry Potter/Magic/Torture Quill

Overview
The Torture Quill is a jet-black quill that cuts whatever is written with it into the user's hand.

Extended Description
It first appears in Harry Potter and the Order of the Phoenix when Professor Umbridge uses it on Harry during his detentions with her. It is described as a "thin, black quill with an unusually sharp point." The purpose of the sharp point is soon revealed, as it turns out to cut whatever is written with it into the back of the user's hand and write the words with the user's blood.

It is later used on Lee Jordan after he attempts to use Educational Decree #26 against her.

On at least one occasion, we see that the scars cut into the back of Harry's hand have remained visible for at least two years, and Harry thinks it unlikely that they will ever completely fade; on another occasion, the scars prickle when Umbridge is recalled to Harry's memory.