The core of Salazar Slytherin’s wand (Pm).
- Isolt Sayre stole Slytherin's wand from her Aunt Gormlaith Gaunt before she fled to Massachusetts on The Mayflower (Pm).
- Years later when Gormlaith arrived at Ilvermorny school to attack Isolt's family, she uttered a single word in Parseltongue which made the Basilisk core of the wand fall into a "sleep," rendering it as useless as a stick. But the same word wakened the Horned River Serpent cores in the wands of the Boot brothers, and their wands suddenly made a "low musical note" as a warning sound, alerting them in time to help fight off Gormlaith Gaunt (Pm).
The implication of the Basilisk horn core is that the wand could hear and understand Parseltongue.