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Harry: "When you say you've got the Cloak, and clothes... "
Hermione: "Yes, they're here."
Ron: "How the ruddy hell – ?"
Hermione: "Undetectable Extension Charm. Tricky, but I think I've done it okay; anyway, I managed to fit everything we need in here."
Hermione Granger explaining her use of the charm in 1997[src]

The Undetectable Extension Charm (incantation unknown) is a charm placed on any object to make the internal space larger than the external object appears. It is possible that it, or similar types of magic are widely used throughout the wizarding world to help conceal the wizarding world from the muggle world.

Known and possible Uses

Hermione Granger used this charm on her small beaded handbag in 1997 so that she was able to pack all the supplies she believed she would need while hunting down Lord Voldemort's Horcruxes with Harry Potter and Ron Weasley. This included books, changes of clothes, money, Harry's Cloak of Invisibility, and healing supplies.[1] Eventually, Hermione also placed the portrait of Phineas Nigellus Black that had previously been in 12 Grimmauld Place in her bag as well[2] to prevent Severus Snape from spying on them.

The same, or a similar, spell was used to make Ministry of Magic cars, tents at the Quidditch World Cup, the Knight Bus, and Alastor Moody's trunk larger on the inside.

This was possibly used also with the Cast-a-Spell Kit because it holds a training room.

It is also possible that it is used to make rooms/ buildings bigger on the inside. A high possibility of such a use is on the Azkaban prison interior in attempt to make room for prisoners. Another possibility of use is to help the concealment of the wizarding world, so the wizards can enjoy large areas inside small recepticles.

Behind the scenes

  • The effects of this spell is similar to the effects of a Bag of Holding in many role playing game scenarios and the TARDIS in Doctor Who.
  • The effects of the spell is also similar to Mary Poppins's carpet bag.

Appearances

Notes and references

  1. Harry Potter and the Deathly Hallows, Ch. 9
  2. Deathly Hallows, Ch. 12
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