|"Are you a wizard or not?"
The title of this article is conjectural. Although it is based on canonical information, the actual name is conjecture and may be supplanted at any time by additional information released from canonical sources. If this occurs, please move this page to the appropriate title.
This spell is a Human Transfiguration spell that transfigures a human into a bat. According to Kennilworthy Whisp, this is one of the few ways wizards may fly unaided, but it is inconvenient due to the fact that a bat does not possess the memory required to remember where one wanted to fly in the first place.
In a 1994 letter to his godfather Sirius Black, Harry Potter noted that the Dursleys were still being uncommonly nice to him that summer because they feared Sirius may suddenly appear and use this spell on them should they misbehave Harry.