Why is Professor McGonagall able to turn into a cat?
Professor McGonagall is a very gifted witch, and a dab hand at Transfiguration (which is useful seeing as it's the subject she teaches at Hogwarts). In fact, she can transfigure herself into a cat! However, not many witches and wizards have this skill, as learning it takes a long time and requires a lot of talent and dedication.
Professor McGonagall is what is known as an Animagus. An Animagus is a witch or wizard who can transform into an animal whenever they want. The process for becoming one is long and tough, with lots of complicated steps. You need to be skilled at Potions, as well as Transfiguration, to have a chance at being successful. Some of the steps include carrying a single Mandrake leaf in your mouth for a month – and if you swallow or remove it you have to start again!
If you make it through the process, you will have the ability to become an animal whenever you choose; however, while you can decide to become an animal, you can’t decide which animal you will become.
Professor McGonagall learned how to become an Animagus while she was still at Hogwarts! It was actually Professor Dumbledore (then a Transfiguration teacher) who taught her how to do this. When she completed all the steps, her Animagus form turned out to be a silver tabby cat, with what appeared to be square spectacle markings around the eyes. McGonagall had these distinctive markings because when you transform, all your clothes and accessories (like glasses) are transformed too – becoming part of your creature’s features.
When witches and wizards are in their animal form, they still retain most of their ability to think like a human, their memories and their human life expectancy. Yet, their emotions are simplified, and they will have many animal instincts – including eating whatever their animal body desires, rather than needing human food.
One other important thing is that all Animagi need to be registered in the Ministry of Magic’s Animagus Registry. All personal details, including what form you take, and any distinctive markings need to be noted. Failure to join the Registry may result in being sent to the wizarding prison Azkaban!
So, Professor McGonagall is a witch with a very rare ability. It is believed that fewer than one in a thousand witches and wizards have this ability! If it goes wrong, the consequences can be dreadful (including half-animal, half-human mutations) and there is no known cure for such mistakes. Which makes Minerva McGonagall’s ability all the more impressive in our eyes!