A Horned Serpent in the creek near Ilvermorny School gave Isolt Sayre the same warning over and over: “Until I am part of your family, your family is doomed” (Pm).
- Isolt had no idea what the warning meant, and wondered if she was just imagining the voice inside her head (Pm). She didn't realize that as a Slytherin descendant through the Gaunt family on her mother's side, Isolt was probably a Parselmouth who could understand the language of snakes.
- Later, the same Horned Serpent gave Isolt part of it's horn to use as wand cores for her two adopted sons, Webster and Chadwick, and thus the Serpent became "part of the family" (Pm).
- When Gormlaith Gaunt attacked the school, she spoke Parseltongue to make the Basilisk core of Isolt's wand go to sleep, but which simultaneously wakened the Horned Serpent cores in the brothers' wands, which began to sound a "low musical note" alerting them to the danger. If that had not occurred, the family certainly would have been "doomed" because Gormlaith could have killed them all as they slept, so the Horned Serpent's warning was true.
Was the Horned Serpent's warning a prophecy? Perhaps, but more likely the Serpent became aware of the Basilisk core inside Isolt Sayre's wand, which had originally belonged to Salazar Slytherin. It's possible the creature instinctively knew the Basilisk wand was susceptible to being put to sleep with Parseltongue, which had the opposite effect on the Horned Serpent cores in the Boot brothers' wands. In that respect, the warning was closer to that of Centaur Divination, since both were done by creatures who were hyper-aware of magical surroundings, as well as reading signs and portents in nature. Just as Firenze warned Harry about the danger of Voldemort in his first year (PS15), the Horned Serpent was trying to help Isolt Sayre and her family.