House-elves

Li Wei heard Headmaster Dumbledore say that, but he still felt the old man was playing dumb again.

"Headmaster, do you really not think Professor Gellert might be another wizard who drank Polyjuice Potion and used a False Disguise to sneak in?"

Dumbledore was stunned when he heard that. Things had already been spelled out this clearly, so why did Li Wei still doubt Grindelwald's identity?

Could he really have caught some flaw in Grindelwald's disguise?

Just because the previous Defense Against the Dark Arts professors had all been bad people, was Li Wei so certain that Grindelwald was bad too?

Though this fellow really was a bad person!

How could Dumbledore have known that Li Wei was simply following the inertia of the plot, guessing that the professor played by Grindelwald was actually Barty Crouch Jr. in disguise?

The two of them were talking past each other, yet somehow everything still lined up.

"That should be impossible," Dumbledore could only do his best to cover for Grindelwald as he explained.

"Li Wei, Polyjuice Potion lasts only a short time. If Professor Gellert were someone else in disguise, he would need to drink the potion constantly!"

"But as you have seen, aside from meals, Professor Gellert rarely drinks or swallows anything, does he?"

Li Wei froze for a moment, then was immediately convinced by Headmaster Dumbledore!

Indeed, when Barty Crouch Jr. had disguised himself as Mad-Eye Moody, he had never been without his flask, taking a sip every now and then.

Professor Gellert, on the other hand, was rarely seen drinking or eating anything apart from at mealtimes.

Without replenishing Polyjuice Potion at regular intervals, Professor Gellert could not be someone else in disguise—unless he was a born Metamorphmagus, or had mastered human Transfiguration to an incredible degree.

For example,