What in the world? Phoenix?

Surely that wasn't an ingredient in this. Those things were rare enough. However, Evelyn couldn't help but wonder if that were really true. And if so, then the professor must have been trying to prove a point about phoenixes or something.

But, back to the question and answers. "Perhaps the bone marrow of a boomslang?" Eh, well the skin of those were used in polyjuice potion and, for some reason, growing bones and turning into someone else, connected in her mind.