In Goblet of Fire,

bad Barty Crouch,

was disguised as

Alastor Moody.

The Polyjuice Potion only lasts for about an hour, as shown in The Chamber of Secrets, and lessons usually last about 1 hour. Why did the disguise not fail during lessons, or why did nobody witness the change?

Does the disguised person take it every time the people leave class?

  • 32
    He carries around and drinks from his flask regularly, most likely also during lessons...
    – BMWurm
    Feb 6, 2016 at 20:03
  • 3
    The flask is not see-through and only the initial change is somewhat troublesome, keeping the form isn't,
    – BMWurm
    Feb 6, 2016 at 20:09
  • 8
    "When the bell finally rang, they hurried out into the corridors towards the Dark Arts classroom, and found Professor Moody leaving it. He looked as tired as they felt. The eyelid of his normal eye was drooping, giving his face an even more lop-sided appearance than usual." - So, yes, after an hour he looks decidedly stressed.
    – Valorum
    Feb 6, 2016 at 20:11
  • 1
    @bleh There's a shot in the film where 'Moody' takes a drink from his hip flask and then grimaces afterwards as though it tasted disgusting. Nobody seemed to notice.
    – Rand al'Thor
    Feb 6, 2016 at 20:27
  • 4
    @randal'thor - I think the insinuation is that they all assume he's drinking some sort of hard liquor. They all look at him like "Weird old drunk." But as students, what are they going to do? Presumably staff may approach Dumbledore, who will be like he was with Snape. "You can trust him, I promise..."
    – ThruGog
    Feb 6, 2016 at 21:04

2 Answers 2


The real Moody is well-known for carrying around a hip flask, and only drinking from it, as to avoid being poisoned. Presumably he will drink from it whenever he wants. Barty Crouch Jr. knew this, and used the hip flask to carry around his Polyjuice Potion, as we see at the end of The Goblet of Fire, when Dumbledore pours out the flask onto the floor. So he would have taken a drink in the middle of class, which would have prevented his un-transformation. That way, he also doesn't change back to Barty and then change to Moody, so he avoids the pain.

Then he picked up the hip flask that stood on the desk, unscrewed it, and turned it over. A thick glutinous liquid splattered onto the office floor.
"Polyjuice Potion, Harry," said Dumbledore. "You see the simplicity of it, and the brilliance. For Moody never does drink except from his hip flask, he's well known for it. The imposter needed, of course, to keep the real Moody close by, so that he could continue making the potion. You see his hair..."

-The Goblet of Fire, Chapter 35 - Veritaserum


Polyjuice potion works for up to twelve hours at a time.

The effect of the potion is only temporary, and depending on how well it has been brewed, may last anything from between ten minutes and twelve hours.

Considering the fact that classes at Hogwarts are less than twelve hours long (I hope), he would have had no problem.

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