Savakka
Посмотрите. И узнала она не от Снейпа. Это зелье не проходят на втором курсе, если я правильно помню

“No, it’s not,” said Hermione. “All we’d need would be some Polyjuice Potion.”
“What’s that?” said Ron and Harry together.
“Snape mentioned it in class a few weeks ago —”

“It wears off after a while,” said Hermione, waving her hand impatiently. “But getting hold of the recipe will be very difficult. Snape said it was in a book called Moste Potente Potions and it’s bound to be in the Restricted Section of the library.”