Muggles' Guide to Harry Potter/Magic/Canary Cream

Overview
Canary Creams, a Weasleys' Wizard Wheezes product, are trick pastries that turns the person eating them briefly into a canary.

Extended Description
Canary Creams outwardly look like custard creams, but have a spell on them that causes the consumer to change into a large canary. The spell lasts only a few seconds, after which time the canary moults, and the victim returns to his normal shape. The first victim is Neville Longbottom, but he is by no means the last; these bewitched treats, sold by Fred and George at seven Sickles apiece, are used extensively in the month between the Triwizard Tournament's First Task and Christmas.

Analysis
Canary Creams seem to play no important part in the story, except perhaps as a prelude to the Skiving Snackbox line that Fred and George will be perfecting in Harry Potter and the Order of the Phoenix. On their own, they are an indication of the type and extent of the twins' magical abilities, and more specifically of the nature of the tricks that they are likely to play.