"Oh - sorry, Neville! ... I forgot - it was the custard..."
"... creams we hexed -"
-- Fred and George Weasley (GF21)
The Canary Transfiguration Hex temporarily changes someone into a giant canary. After a few moments, the Transfigured person molts back into themselves.
References from the canon
- Fred and George placed this hex on seemingly innocent custard creams so that whomever ate one was changed temporarily into a huge canary. Neville ate one of these Canary Creams, much to the amusement of everyone in the Gryffindor common room (GF21).
Jinxes and hexes
From the Web
"Canary Cream" from Harry Potter Wiki