Basilisk parts

Fangs and venom from the dreaded giant serpent that once lived in the Chamber of Secrets have magical properties.

• The fangs of the Basilisk are filled with deadly poison (FB).
• Harry was pierced by one in the Chamber of Secrets and would have died if not for the tears of Fawkes the phoenix (CS17). He also discovered that a fang could be used to destroy Tom Riddle's diary, a Horcrux. In fact, Basilisk venom is the one "foolproof" way to destroy a Horcrux, according to Hermione (DH6).
• The Horcrux inside Harry's scar was not destroyed by the Basilisk venom because "The Horcrux-receptacle has to be destroyed beyond repair, so Harry would need to have DIED" (JKR:Tw).
• The Sword of Gryffindor was "impregnated with basilisk venom" after it was used to kill the basilisk in the Chamber of Secrets, since "[g]oblin-made blades imbibe only that which can strengthen them" (DH15).
• After the Battle of Hogwarts, Ron Weasley and Hermione Granger gathered more fangs and used them to destroy another Horcrux, the Hufflepuff Cup (DH31).
• Salazar Slytherin's wand contained a Basilisk horn core which could still understand Parseltongue; Gormlaith Gaunt used a word meaning "wand sleep" to render it useless when she attacked Isolt Sayre's family at Ilvermorny School (Pm).