Secrets of the Darkest Art - by Owle Bullock
Includes how to make a Horcrux. Copy owned by Pecival Graves. Contents borrowed by Pottermore with small alterations. Reviews: "This is the one that gives explicit instructions on how to make a Horcrux. Secrets of the Darkest Art — it's a horrible book, really awful, full of evil magic" —Hermione Granger. "I found it on a law-breaking miscreant -- yes I plan to report it, it is obviously not mine." - Percival Graves
Parseltongue & Summoning the Dark Mark
Parseltongue is the language of serpents as well as other magical serpent-based creatures, like the Runespoor and those who can converse with them. An individual who can speak Parseltongue is known as a Parselmouth. It is a very uncommon skill, and is typically hereditary. Nearly all known Parselmouths are descended from Salazar Slytherin. While inherited, Parseltongue usually requires the speaker to face a snake-based creature or object shaped like a snake e.g. a carving; more proficient speakers may be able to speak it at will.
Parseltongue is, when spoken, a hissing sound, similar to that of a snake; as such, normal people cannot understand it. Aside from serpent-based creatures, Parselmouths can communicate with each other with the language, and this can used as a secret ways of communication..
Phillipus Aureolus Theophrastus Bombastus von Hohenheim 1493 - 1541, more commonly known as Paracelsus, was a secretive alchemist credited with the discovery of Parseltongue.
Summoning The Dark Mark - Morsmorde -
The Dark Mark is the symbol of Lord Voldemort and his Death Eaters. It refers both to a magically induced brand that every Death Eater bears on his or her inner left forearm. The incantation of the dark mark depicts a green serpent entwined skull that is cast over the homes of anyone the Death Eaters kill or as a threat of murder, a sign of dark unabridged power meant to spread fear.