Index · potion · book 2
Polyjuice Potion
A slow brew that lets the drinker borrow another person’s appearance. It does not borrow their knowledge.
Polyjuice takes weeks and a piece of the person you mean to resemble. The result is a body double with a time limit. Students in the second year attempt it as a detective scheme. Later the potion becomes a tool of infiltration, including uses that are no longer a school prank.
Appearance is not identity. The books enjoy the gap: the walk is wrong, the voice slips, the knowledge you needed was never in the flask. Canon fact: the potion changes the body for a while. The moral mess is in how it is used.