Canary Creams are one of the joke products that Fred and George Weasley invented for their shop, Weasleys' Wizard Wheezes. They created them in 1994 and charged seven Sickles for each. They have the appearance and taste of ordinary custard creams, but when eaten, they transfigure the eater into a large canary. Within a minute, the person will moult his or her feathers and revert to normal appearance.
Neville Longbottom ate one during a celebration party for Harry Potter's triumph over the Hungarian Horntail in the First Task of the Triwizard Tournament. He had just bitten into it when he overheard Fred offering Hermione Granger a jam tart and telling her that the tarts were not hexed, but the custard creams were. Neville immediately spat the food out, but was gullible enough to believe one of the twins was only joking, returning to the consumption of the canary creams. He soon caused a diversion by turning into a large canary. Within a minute, he reverted back, and joined in the laughter.