Magical abilities
Animagi transformation
An Animagus (portmanteau of animal and magus) is a witch or wizard who can turn into a particular animal or magical creature at will. This ability is not innate: it must be acquired by magical means. All Animagi must register at a central authority; it is illegal to obtain this ability without registering, although out of the five Animagi described as such in the books (Minerva McGonagall, Rita Skeeter, James Potter, Sirius Black and Peter Pettigrew), only McGonagall is mentioned as a registered Animagus.
Animagi transformation is one of the few forms of magic that can be performed deliberately wandlessly. This is exemplified when both Sirius and Peter are left wandless for over 10 years, both retaining the ability with supposedly no ill effects. When Animagi transform, the animal appears to be a normal animal. However, during Prisoner of Azkaban, it is noted that Ron's pet rat Scabbers (later revealed as Peter Pettigrew's Animagus form) has lived over twelve years when only expected to live three. Also, an Animagus in animal form retains the ability to think like a human, which is the principal difference from being an animagus and being transfigured into an animal. Characteristics of an Animagus' human form can manifest themselves in the animal transformation: general appeararance of both Pettigrew and Sirius Black, markings around McGonagall's eyes that resemble her glasses, Pettigrew missing a toe from one paw to match the finger he cut off, and so on.
Each Animagus has a specific animal form, and cannot transform into any other animal. The animal cannot be chosen: it is uniquely suited to that individual's personality, like the Patronus Charm, and in most cases the Animagus will change into the same animal used in the person's Patronus charm. (McGonagall's Patronus is a cat, like her Animagus form; James Potter's was a stag, which was also his Animagus form.) Similarly, when an Animagus transforms it is always into the same animal (i.e. same markings, same colours, etc.). When an Animagus registers, they must record all the defining physical traits of their animal form so that the Ministry can identify them.
Explicit emphasis is made in the books on the differences between Animagi and werewolves. Animagi have full control over their transformations and retain their minds, whereas werewolves' transformations are involuntary and include severe changes in personality. After the person has transformed into a werewolf, he no longer remembers who he is; he would kill his best friend if he got anywhere near him. A werewolf only responds to the call of his own kind. The only way that a werewolf can retain his sanity, intelligence and memory while transformed is using the Wolfsbane Potion.
Rowling also makes it clear in The Tales of Beedle the Bard that an animagus is not the same as a wizard simply transfiguring themselves into an animal. The former ability, as mentioned above, allows the witch or wizard to maintain their own mind and human powers of reasoning and memory. The latter, however, would cause the person to gain the brain of the animal they have transfigured into. This would lead to the obvious problem that they would forget that they were a wizard and be trapped, unknowingly, in this form for the rest of that creature's lifespan unless transformed back by another wizard.
Animagi transformation is one of the few forms of magic that can be performed deliberately wandlessly. This is exemplified when both Sirius and Peter are left wandless for over 10 years, both retaining the ability with supposedly no ill effects. When Animagi transform, the animal appears to be a normal animal. However, during Prisoner of Azkaban, it is noted that Ron's pet rat Scabbers (later revealed as Peter Pettigrew's Animagus form) has lived over twelve years when only expected to live three. Also, an Animagus in animal form retains the ability to think like a human, which is the principal difference from being an animagus and being transfigured into an animal. Characteristics of an Animagus' human form can manifest themselves in the animal transformation: general appeararance of both Pettigrew and Sirius Black, markings around McGonagall's eyes that resemble her glasses, Pettigrew missing a toe from one paw to match the finger he cut off, and so on.
Each Animagus has a specific animal form, and cannot transform into any other animal. The animal cannot be chosen: it is uniquely suited to that individual's personality, like the Patronus Charm, and in most cases the Animagus will change into the same animal used in the person's Patronus charm. (McGonagall's Patronus is a cat, like her Animagus form; James Potter's was a stag, which was also his Animagus form.) Similarly, when an Animagus transforms it is always into the same animal (i.e. same markings, same colours, etc.). When an Animagus registers, they must record all the defining physical traits of their animal form so that the Ministry can identify them.
Explicit emphasis is made in the books on the differences between Animagi and werewolves. Animagi have full control over their transformations and retain their minds, whereas werewolves' transformations are involuntary and include severe changes in personality. After the person has transformed into a werewolf, he no longer remembers who he is; he would kill his best friend if he got anywhere near him. A werewolf only responds to the call of his own kind. The only way that a werewolf can retain his sanity, intelligence and memory while transformed is using the Wolfsbane Potion.
Rowling also makes it clear in The Tales of Beedle the Bard that an animagus is not the same as a wizard simply transfiguring themselves into an animal. The former ability, as mentioned above, allows the witch or wizard to maintain their own mind and human powers of reasoning and memory. The latter, however, would cause the person to gain the brain of the animal they have transfigured into. This would lead to the obvious problem that they would forget that they were a wizard and be trapped, unknowingly, in this form for the rest of that creature's lifespan unless transformed back by another wizard.
Metamorphmagi
A Metamorphmagus (a portmanteau of metamorph and magus) is a witch or wizard born with the innate ability to change some or all of their appearance at will. The talent cannot be acquired; a witch or wizard who has it must be born with it.
Nymphadora Tonks and her son, Teddy Lupin are currently the only known Metamorphmagi in the series; it is a very rare ability, possibly hereditary. Tonks is known to change her hair colour and style according to her mood. Indeed, she even appears as an old woman on occasion. She can also change her nose appearance, as she does when eating with the Weasley family to entertain Ginny and Hermione. Her son, Teddy Lupin, also inherited this trait, as his hair is mentioned repeatedly changing colour.
The extent of these appearance-altering abilities and the limits thereof are not entirely clear. According to Rowling, a Metamorphmagus can alter his or her appearance completely, for instance, from black to white, young to old, handsome to plain and so on. In one example, Tonks changes her facial appearance by reshaping her nose into "a beaklike protuberance like Snape's", to "something resembling a button mushroom", and "one like a pig snout" which reminded Harry of his cousin Dudley.
Nymphadora Tonks and her son, Teddy Lupin are currently the only known Metamorphmagi in the series; it is a very rare ability, possibly hereditary. Tonks is known to change her hair colour and style according to her mood. Indeed, she even appears as an old woman on occasion. She can also change her nose appearance, as she does when eating with the Weasley family to entertain Ginny and Hermione. Her son, Teddy Lupin, also inherited this trait, as his hair is mentioned repeatedly changing colour.
The extent of these appearance-altering abilities and the limits thereof are not entirely clear. According to Rowling, a Metamorphmagus can alter his or her appearance completely, for instance, from black to white, young to old, handsome to plain and so on. In one example, Tonks changes her facial appearance by reshaping her nose into "a beaklike protuberance like Snape's", to "something resembling a button mushroom", and "one like a pig snout" which reminded Harry of his cousin Dudley.
Parseltongue
Parseltongue is the language of snakes. It is designed by Professor Francis Nolan, who is currently teaching at University of Cambridge, for the films. It is, in the common mind, associated with Dark Magic (although Dumbledore stated that it is not necessarily an evil quality), and those possessing the ability to speak it ("Parselmouths") are very rare. It appears to be a skill acquired through learning or via a method of xenoglossia, such as through genetic inheritance (or by use of Dark or dangerous Magic). Harry is a Parselmouth: it is revealed in Harry Potter and the Chamber of Secrets to be due to Voldemort's passing on some of his abilities to Harry the night he tried to kill him. In Deathly Hallows it is revealed that it is a part of Voldemort's soul within Harry that grants him this ability, which is later destroyed leaving Harry stripped of the ability.
Other known Parselmouths include: Salazar Slytherin and his descendants, including the Gaunts and Voldemort. Dumbledore can also understand Parseltongue; however, he learnt it and did not naturally possess the ability. In Half-Blood Prince he repeats Morfin Gaunt's words "the big house over the way", which were spoken in Parseltongue.
Ron uses Parseltongue in the final book to reopen the Chamber of Secrets, but he is only copying a phrase Harry used earlier in the book.
Rowling borrowed the term from "an old word for someone who has a problem with the mouth, like a hare lip".
Other known Parselmouths include: Salazar Slytherin and his descendants, including the Gaunts and Voldemort. Dumbledore can also understand Parseltongue; however, he learnt it and did not naturally possess the ability. In Half-Blood Prince he repeats Morfin Gaunt's words "the big house over the way", which were spoken in Parseltongue.
Ron uses Parseltongue in the final book to reopen the Chamber of Secrets, but he is only copying a phrase Harry used earlier in the book.
Rowling borrowed the term from "an old word for someone who has a problem with the mouth, like a hare lip".
Seers
A Seer is a witch or wizard with the clairvoyant ability to predict future events. The predictions given through this ability can sometimes be self-fulfilling prophecies, and Dumbledore states in Order of the Phoenix that not all of them come true, depending on the choices made by those mentioned. This would seem to indicate that a Seer predicts possible or likely events, at least in some cases. Sybill Trelawney is noted to never remember that she has made a prophecy when it is a true one. She speaks in a hoarse voice and only if a wizard is present will anyone know about it.
In the Hall of Prophecy at the Department of Mysteries, thousands upon thousands of glass spheres are imbued with records of prophecies made by Seers. Only a person mentioned in a prophecy can safely retrieve it; anyone else who tries to do so will be driven insane.
According to McGonagall, true Seers are extremely rare. Sybill Trelawney is the only Seer portrayed in the books, although it is mentioned that Sybill's great-great-grandmother, Cassandra Trelawney, was a renowned Seer in her day. Trelawney is considered an "old fraud" by her students, and is sacked by Dolores Umbridge in the fifth book for it. However, she has twice made true prophecies (not counting minor predictions such as Neville's breaking a teacup). It is unclear whether Trelawney's visions of the Grim 'following' Harry in his third year are Sirius Black in Animagus form or just Trelawney being melodramatic and predicting the tragic death of a student as she has done every year.
In an ironic twist, however, when looked over in hindsight after reading the books, all of Trelawney's predictions (for example predicting Harry Potter and Remus Lupin's death - though the former was only through a technicality) come true eventually.
In the Hall of Prophecy at the Department of Mysteries, thousands upon thousands of glass spheres are imbued with records of prophecies made by Seers. Only a person mentioned in a prophecy can safely retrieve it; anyone else who tries to do so will be driven insane.
According to McGonagall, true Seers are extremely rare. Sybill Trelawney is the only Seer portrayed in the books, although it is mentioned that Sybill's great-great-grandmother, Cassandra Trelawney, was a renowned Seer in her day. Trelawney is considered an "old fraud" by her students, and is sacked by Dolores Umbridge in the fifth book for it. However, she has twice made true prophecies (not counting minor predictions such as Neville's breaking a teacup). It is unclear whether Trelawney's visions of the Grim 'following' Harry in his third year are Sirius Black in Animagus form or just Trelawney being melodramatic and predicting the tragic death of a student as she has done every year.
In an ironic twist, however, when looked over in hindsight after reading the books, all of Trelawney's predictions (for example predicting Harry Potter and Remus Lupin's death - though the former was only through a technicality) come true eventually.
Legilimency and Occlumency
Legilimency is the magical skill of extracting feelings and memories from another person's mind — a form of magical "telepathy" (although Snape, an able practitioner of the art, dismisses the colloquial term, "mind-reading", as a drastic oversimplification). It also allows one to convey visions or memories to another person, whether real or imaginary. A witch or wizard possessing this skill is called a Legilimens, and can, for example, detect lies and deceit in another person, witness memories in another person's past, or "plant" false visions in another's mind.
The counter-skill to Legilimency is Occlumency (and its user, known as an Occlumens), by which one can compartmentalise one's emotions, or prevent a Legilimens from discovering thoughts or memories which contradict one's spoken words or actions. An advanced form of Occlumency is planting false temporary memories inside an Occlumens´ own head while blocking all other true memories, so if a Legilimens, even a highly skilled one, were to attempt to read the mind he or she would find false memories only and believe everything was right. This is how Snape was able to lie to Voldemort for years.
Voldemort, Snape, and Dumbledore are all known to be skilled in Legilimency and Occlumency. Throughout the books, Snape is repeatedly said to be highly skilled in Occlumency. Voldemort is said to be the master of Legilimency by Snape, as he, in almost all cases, immediately knows during conversations if someone lies to him.
The skills are first mentioned in Order of the Phoenix, (though Harry gets the impression before that Snape can read minds) wherein Snape is instructed by Dumbledore to give Harry lessons in Occlumency. Whether as a result of negligence in Snape's instruction, or poor aptitude on Harry's part, Harry never made any progress in the skill, and as a result he was lured by Voldemort through a carefully calculated vision he falsely believed to be real. Only once has Harry managed to overcome Snape with the use of Occlumency, in Order of the Phoenix. It seems that not everyone is able to master Occlumency. Also, although it appears to be an advanced form of magic, a young wizard can learn to be an Occlumens (Draco Malfoy was able to block Snape's attempt to use Legilimency on him in his 6th year, after being taught Occlumency by Bellatrix Lestrange). Near the end of Order of the Phoenix, Harry learns from Dumbledore that his love for Sirius is what caused Voldemort to release his possession of Harry. Revolting from the love in Harry, Voldemort feared the further use of Legilimency on Harry, drawing away from their connection. This allows Harry to freely see/feel Voldemort's thoughts/emotions in the next two books. In Deathly Hallows, Harry finally does master Occlumency - shutting his mind to Voldemort - when Dobby dies. He realises that his grief - or what Dumbledore calls it, love - is what can block out the Dark Lord.
Bellatrix Lestrange, Draco Malfoy, Narcissa Malfoy and Barty Crouch, Jr also have skill in Occlumency, since Bellatrix was clearly said to have taught Draco to shield his thoughts from Snape. It was never clearly said that Narcissa was an Occlumens, but since she successfully managed to prevent Voldemort (the master of Legilimency) from detecting her lie about Harry's death, she is very likely to be one.
Legilimency and Occlumency are not part of the normal curriculum at Hogwarts, and most students would graduate without learning them. They seem to be considered a more advanced form of magic.
The counter-skill to Legilimency is Occlumency (and its user, known as an Occlumens), by which one can compartmentalise one's emotions, or prevent a Legilimens from discovering thoughts or memories which contradict one's spoken words or actions. An advanced form of Occlumency is planting false temporary memories inside an Occlumens´ own head while blocking all other true memories, so if a Legilimens, even a highly skilled one, were to attempt to read the mind he or she would find false memories only and believe everything was right. This is how Snape was able to lie to Voldemort for years.
Voldemort, Snape, and Dumbledore are all known to be skilled in Legilimency and Occlumency. Throughout the books, Snape is repeatedly said to be highly skilled in Occlumency. Voldemort is said to be the master of Legilimency by Snape, as he, in almost all cases, immediately knows during conversations if someone lies to him.
The skills are first mentioned in Order of the Phoenix, (though Harry gets the impression before that Snape can read minds) wherein Snape is instructed by Dumbledore to give Harry lessons in Occlumency. Whether as a result of negligence in Snape's instruction, or poor aptitude on Harry's part, Harry never made any progress in the skill, and as a result he was lured by Voldemort through a carefully calculated vision he falsely believed to be real. Only once has Harry managed to overcome Snape with the use of Occlumency, in Order of the Phoenix. It seems that not everyone is able to master Occlumency. Also, although it appears to be an advanced form of magic, a young wizard can learn to be an Occlumens (Draco Malfoy was able to block Snape's attempt to use Legilimency on him in his 6th year, after being taught Occlumency by Bellatrix Lestrange). Near the end of Order of the Phoenix, Harry learns from Dumbledore that his love for Sirius is what caused Voldemort to release his possession of Harry. Revolting from the love in Harry, Voldemort feared the further use of Legilimency on Harry, drawing away from their connection. This allows Harry to freely see/feel Voldemort's thoughts/emotions in the next two books. In Deathly Hallows, Harry finally does master Occlumency - shutting his mind to Voldemort - when Dobby dies. He realises that his grief - or what Dumbledore calls it, love - is what can block out the Dark Lord.
Bellatrix Lestrange, Draco Malfoy, Narcissa Malfoy and Barty Crouch, Jr also have skill in Occlumency, since Bellatrix was clearly said to have taught Draco to shield his thoughts from Snape. It was never clearly said that Narcissa was an Occlumens, but since she successfully managed to prevent Voldemort (the master of Legilimency) from detecting her lie about Harry's death, she is very likely to be one.
Legilimency and Occlumency are not part of the normal curriculum at Hogwarts, and most students would graduate without learning them. They seem to be considered a more advanced form of magic.