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"At once, the statue's hump opened wide enough to admit a fairly thin person."

—Description^[src]

Dissendium was the incantation of a charm that revealed hidden passageways.

Known practitionersEdit

While initially this appears to be a simple password for the statue, it was used in other media in attempts to open lockets, out of frustration.
It is unknown what may happen if Dissendium is used on something else besides passageways, for example it caused a small explosion when it was used in a failed attempt to destroy the locket.

↑ ^1.0 ^1.1 Seeing how he knew of the passage and where it led, it is more than likely he used it. And as one had to perform this spell, to use it, he thus used the spell.
↑ Harry Potter and the Prisoner of Azkaban (Chapter Fourteen - Snape's Grudge)
↑ Hermione retrieved Harry's cloak from beneath the One-Eyed Witch; she needed to have cast Dissendium to open the passage