system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] Polyjuice Potion unlimited supply

I'll use Barty Crouch as an example:  Did he need to keep Moody alive? or was he able to use polyjuice to turn into moody, and whilst being fake moody pluck his own hair to use for the next potion?
gpt
He had to keep Moody alive to get raw materials for the potion - his own hair, even though it was morphed to look like Moody's, wasn't actually Moody's - such magic works on internal essence, not external appearance.