Moste Potente Potions?

"Moste Potente Potions?" she repeated suspiciously, trying to take the
note from Hermione; but Hermione wouldn't let go.

"I was wondering if I could keep it," she said breathlessly.

"Oh, come on," said Ron, wrenching it from her grasp and thrusting it
at Madam Pince. "We'll get you another autograph. Lockhart'll sign
anything if it stands still long enough."

Madam Pince held the note up to the light, as though determined to
detect a forgery, but it passed the test. She stalked away between the
lofty shelves and returned several minutes later carrying a large and
moldy-looking book. Hermione put it carefully into her bag and they
left, trying not to walk too quickly or look too guilty.

Five minutes later, they were barricaded in Moaning Myrtle's out-of-
order bathroom once again. Hermione had overridden Ron's objections
by pointing out that it was the last place anyone in their right minds
would go, so they were guaranteed some privacy. Moaning Myrtle
was crying noisily in her stall, but they were ignoring her, and she
them.

Hermione opened Moste Potente Potions carefully, and the three of
them bent over the damp-spotted pages. It was clear from a glance
why it belonged in the Restricted Section. Some of the potions had
effects almost too gruesome to think about, and there were some very
unpleasant illustrations, which included a man who seemed to have
been turned inside out and a witch sprouting several extra pairs of
arms out of her head.

"Here it is," said Hermione excitedly as she found the page headed The
Polyjuice Potion. It was decorated with drawings of people halfway
through transforming into other people. Harry sincerely hoped the artist
had imagined the looks of intense pain on their faces.