Muggles' Guide to Harry Potter/Magic/Animagus

Overview
An Animagus is a witch or wizard with the rare ability to transform into a particular animal at will. The Animagus spell is very difficult and dangerous to perform, which is one reason that all Animagi are required to be registered by the Ministry of Magic. Another reason is so the Ministry can ensure that an Animagus does not use his or her power for any illegal purpose while in their animal forms.

Extended Description
While the term is only presented and defined in Harry Potter and the Prisoner of Azkaban, the ability of some witches or wizards to change into the shape of animals is seen in the very first chapter of Harry Potter and the Philosopher's Stone. Here, Professor Dumbledore addresses a tabby cat as Professor McGonagall, and finds a woman sitting there when he looks again. Animagi are extremely rare. It is revealed that Professor McGonagall is one of the only seven registered Animagi of the century.

However, we know of four unregistered Animagi: Peter Pettigrew (Wormtail), who can transform into a rat, Sirius Black, who can turn into a large, black dog, James Potter, who transformed into a stag, and Rita Skeeter, who becomes a beetle.

The Animagus transformation is one of a very few forms of magic that can be performed in a controlled manner without a Wand. Sirius and Wormtail have displayed the ability to transform into their Animagus shapes without wands.

There is no mention of anything that can prevent an Animagus from transforming, wandless or otherwise; however, there is apparently a spell, identified outside of canon as the Homorphus Charm, which can be used to force a transformed Animagus back into his human shape. We see this charm used by Sirius Black and Remus Lupin to reveal Peter Pettigrew to the Trio. We note that the spell was cast by Lupin and Black simultaneously; this may have been necessary to increase the strength of the spell. One wizard casting the spell might not be enough to force the conversion, unless the targeted wizard was magically significantly weaker than the casting wizard.

Analysis
James Potter, Sirius Black, and Peter Pettigrew all became Animagi after discovering that their friend Remus Lupin was a Werewolf. Because a werewolf is only a danger to humans, they decided that they could keep him company during his transformations by turning into animals. They used their power to wander around the Hogwarts grounds at night, while Lupin was in his wolf form.

Rita Skeeter, who is a reporter, became an Animagus perhaps so that she would be able to spy on people to get good stories for the papers she writes for, notably the Daily Prophet and Witch Weekly. Note that the witch or wizard performing the spell does not have control over the specific type of animal he will become; the form that the wizard's animal form takes will depend on his personality at the time he performs the spell. The fact that Rita became a beetle, so very close to the proverbial "fly on the wall", could only be providential – she could not have selected for it.

One must assume that the main purpose for a wizard to choose to become an Animagus is as a way of transforming into an innocuous beast, so as to avoid recognition while acting illegally. It is for this reason that the Ministry requires that all Animagi be registered, so that any Transformed wizard who chooses to act illegally may be identified.

As mentioned in The Tales of Beedle the Bard (in Dumbledore's notes on "Babbitty Rabbitty and her Cackling Stump"), the Animagus transformation is a form of Transfiguration. There is a difference, though; a wizard who is Transfigured into an animal is fully an animal, with the animal's brain, comprehension, and abilities, which means that he must perforce remain an animal until some other wizard Transfigures him back into his original self. Following the Animagus transformation, the wizard retains his own original intellect and abilities, undiminished, and so can transform himself back to human.

It should perhaps be mentioned that Professor McGonagall has never done anything unlawful while in her Animagus state. Her sole reason for becoming Animagus was as part of her studies of Transfiguration.

Questions

 * 1) If a wizard performs the Animagus spell twice, can he or she then change into two different types of animal? Or would it change the type of animal he or she could transfigure into? Why?
 * 2) Could a wizard's Animagus form be the same as their Patronus?
 * 3) Could a wizard's Animagus form change from emotional trauma, as a patronus can?
 * 4) To become an Animagus, would you be more likely to use a spell or a potion?
 * 5) Do you choose the animal you transform into?
 * 6) Could a metamorphmagus who became an Animagus change the way they looked when transformed?

Greater Picture
It should, perhaps, be mentioned that in fact there is one wizard we see who displays both Animagus and Patronus forms. In Harry Potter and the Deathly Hallows, Professor McGonagall sends off three Patronuses to summon the three other Heads of House. These Patronuses, it should be noted, take the same shape as her Animagus form — tabby cats. Thus, it is safe to assume that the Animagus shape and the Patronus shape would be the same, if the two spells were cast at the same time. However, the Animagus spell (as opposed to the transform) is apparently an enabling spell, that allows the transformation to be made at will. What little information we have leads us to believe that the Animagus form is fixed once the spell is cast, while the Patronus can change due to life changes; both the Patronus and the Animagus forms reflect the personality at the time the spell was cast, but the Patronus spell is cast repeatedly while the Animagus is generally performed only once.