Flight (without broom or other means of transportation), Occlumency, Legilimency
Professor Severus Snape is the Potions master and head of Slytherin house, and is seen as the main secondary antagonist up until the end of the first book. His most notable appearance is during Chapter 8, which is named after him ("The Potions Master"). He teaches in the dungeons' Potions Classroom.
Professor Snape looks straight at Harry during the feast, causing a sharp, hot pain to shoot through Harry's scar. Snape teaches potions at Hogwarts, but Percy tells Harry it is well known that Snape really wants to teach Defence Against the Dark Arts.
During the start-of-term feast, Percy tells Harry that Professor Snape knows an awful lot about Dark magic, and that it’s widely known that Professor Snape would rather teach Defence Against the Dark Arts than his own subject.
Professor Snape’s dislike for Harry becomes obvious during the first Potions lesson of the year, in which he singles Harry out, firing questions at him; he sneers when Harry doesn’t know the answers and takes points from Gryffindor for Harry’s cheeky retort.
After Hallowe’en, Professor Snape is seen limping and, later, nursing a wound given to him by the three-headed dog on the third-floor corridor. As a result, Harry and Ron begin to believe this is because he is trying to get past the creature to the trapdoor underneath. He also appears to be trying to jinx Harry off his broom during the Gryffindor versus Slytherin Quidditch match, which finally convinces Hermione that he is up to something.
Professor Snape was not, as Harry initially thought, the person who was trying to steal the Philosopher’s Stone or jinx Harry off his broom. He was trying to protect the Stone by intimidating Professor Quirrell and was attempting to save Harry’s life by muttering a counter to Professor Quirrell’s jinx during the Quidditch match.
At the end of the year Professor Snape’s feelings toward Harry don’t seem to have changed one bit.
Professor Snape confronts Harry and Ron on the Hogwarts grounds after they land at school, and takes them into the castle, smiling grimly about their fate. After bringing the boys inside, Snape takes Harry and Ron to his office and lectures them about their flight. He then brings Professor McGonagall to the office.
On the first Saturday of the year, Snape gives the Slytherin team permission to book the Quidditch pitch (over Gryffindor’s existing booking), owing to the group’s need to train their new Seeker, Draco Malfoy.
Snape seems to know that Harry had something to do with the disruption in his class caused by an exploding firework. He gives Harry a look that suggests he can read his mind.
Snape and Professor Lockhart run the Duelling Club. Snape disarms Lockhart so effectively that the Defence Against the Dark Arts teacher is blasted across the room. He also suggests pairing Harry and Draco as duelling partners and volunteers them to demonstrate how to block unfreindly spells.
Snape is less than impressed at Lockhart's Valentine's Day celebrations, in fact he looks like he has been fed a beaker of Skele-Gro and will force-feed poison to the first person who takes Lockhart's advice to ask him about how to whip up a Love Potion..
In the potions lesson before Defense Against the Dark Arts, Professor Snape orders Harry and Ron to help an apparently wounded Draco prepare his potion ingredients. Snape spends much of the lesson terrorising Neville, and orders Hermione not to help Neville fix his unsuccessful potion. At the end of the class, Snape carries out his threat to demonstrate Neville's potion on Neville's toad Trevor, assuming that Neville has failed to correctly make the potion. When Neville's potion works perfectly, Snape deducts five points from Gryffindor to punish Hermione for helping Neville against his instructions. In the staff room, Snape continues to bully Neville, telling Professor Lupin not to entrust him with anything difficult. He leaves the staff room before the lesson begins, not wanting to watch the students face the Boggart in the wardrobe.
Snape enters Lupin's office carrying a goblet that is smoking faintly. He sets the goblet down on Lupin's desk, and tells Lupin that he must drink the potion immediately. He mentions that he has made an entire cauldronful of the potion, should Lupin need more. During the Hallowe'en feast, Snape seems to glance over at Lupin more often than is usual.
Snape arrives at the portrait of the Fat Lady with Professor McGonagall and Professor Lupin.
After Peeves informs Dumbledore that it was Black that attacked the Fat Lady's portrait, Snape helps to search the castle. When he returns to the Great Hall, Snape tells Dumbledore that the dungeons and third floor have been searched, and that Black is not there. He reminds Dumbledore of a conversation they had before the start of term, and suggests that Black could have an accomplice inside Hogwarts. He doesn't reply to Dumbledore's vehement denial, and soon leaves the Great Hall.
The day before the Quidditch match, Snape takes Lupin's third-year Defense Against the Dark Arts lesson as Lupin says he is too ill to teach that day. When Harry enters the classroom ten minutes late, Snape deducts ten points from Gryffindor and a further five when Harry does not sit down as he is told. Snape is dismissive of Lupin's abilities as a teacher, and tells the class that they will be studying werewolves. He fires questions at the students, but ignores Hermione's attempts to answer them. At the end of the lesson he sets the class an essay on the methods of recognising and killing werewolves.
Professor Snape finds Harry and Neville in the third-floor corridor. He asks them why they are meeting in such an odd place, and tells them to make their way back to Gryffindor Tower. As they leave, Snape examines the statue of the one-eyed witch closely, but eventually returns to his office.
Snape finds Harry by the statue of the one-eyed witch once more and escorts Harry to his office to tell him that Draco Malfoy has attested that he saw Harry's head in Hogsmeade. Snape is convinced that Harry has found a way into Hogsmeade, and attempts to provoke Harry into telling him the truth. As their confrontation becomes heated, Snape demands that Harry empty his pockets. Picking up the Marauder's Map, he asks why Harry needs such an old piece of parchment. He taps the map, demanding that it reveal its secrets. He freezes as he reads the insulting messages that appear on the map's surface, then strides across to his fire and summons Professor Lupin, convinced that the map is full of Dark Magic.
Lupin tells the trio that the brew Snape has been making for him is Wolfsbane Potion. He tells them that Snape was at Hogwarts at the same time as him and his friends. Snape fought hard against Lupin's appointment as Defence Against the Dark Arts teacher, and has been telling Dumbledore all year that Lupin is not to be trusted.
When Snape, Lupin, James Potter, Sirius Black and Peter Pettigrew were at Hogwarts, Snape caught sight of Madam Pomfrey escorting Lupin to the Whomping Willow one evening. He was told how to immobilise the Whomping Willow by Black, as a cruel practical joke, and managed to get into the tunnel. Snape was pulled away to safety just in time by James, but caught a glimpse of Lupin in his werewolf form at the end of the tunnel. He was forbidden by Dumbledore to tell anybody, but has known what Lupin was since that day.
Snape reveals himself to be in the room after Lupin has finished telling the others about Black's prank, having used the Invisibility Cloak to enter the Shrieking Shack undetected.
Snape throws the Invisibility Cloak aside, and thanks Harry for unwittingly leaving it at the base of the Whomping Willow. He tells Lupin that he had gone to his office with a goblet of the Wolfsbane Potion and saw the Marauder's Map on Lupin's desk. Snape saw Lupin marked on the Map, running along the passageway from the Whomping Willow. He is convinced that Lupin has been helping Sirius Black into the castle, and is triumphant that he finally has his proof. His eyes gleam fanatically as he talks of Lupin and Black going to Azkaban, and he wonders aloud what Dumbledore will think about Lupin's betrayal of his trust. Snape conjures ropes to restrain Lupin when his colleague tries to reason with him. Snape aims his wand straight between Sirius's eyes when Sirius starts to lunge at him. He tells Sirius he won't hesitate to use his wand against him if given the chance. It is impossible to tell who hates the other more as they glare at each other.
When Hermione attempts to reason with Snape, he tells her to hold her tongue, and loses his temper when she persists. His attitude is triumphant as he talks to Black, as he had hoped to be the one to catch him. Snape tells Black that he doesn't think they need return to the castle, as he can merely call the Dementors once the group exit the passageway at the Whomping Willow. He enjoys tormenting Black with the thought of the Dementor's Kiss. Snape shouts furiously at Harry when he attempts to block his way. Before he can take a step towards Harry, he is hit by three simultaneous Expelliarmus spells from Harry, Ron and Hermione, and is thrown backwards into the wall by the force. He lies unconscious at the foot of the wall, blood oozing from under his hair.
When the group prepare to leave the Shrieking Shack, Snape is taken with them, his unconscious body controlled by the incantation Mobilicorpus, performed by Lupin.
Snape stands in the corridor just outside the hospital wing talking to Cornelius Fudge. He explains to Fudge that after regaining consciousness he found Harry, Hermione and Sirius at the lake and brought them back to the castle, along with Ron, on conjured stretchers. He uses the opportunity to criticise Dumbledore's leniency towards Harry, and tells Fudge that he suspects Harry has been visiting Hogsmeade illegally, on top of his other offences. He doesn't know what drove the Dementors away, and tells Fudge that they were heading back to their positions at the school entrances when he arrived.
Snape enters the hospital wing with Fudge after he hears Harry shouting. He tells Fudge that Harry's claims about the events that night are proof that Sirius used the Confundus Charm on the them. He grows irritated when Dumbledore does not immediately dismiss Harry's story, and feels that his own evidence is being discounted. Just before he leaves the hospital wing, Snape asks Dumbledore whether he really believes Sirius's story. He reminds Dumbledore that Sirius once nearly killed him, and believes this is proof that Black is capable of murder. He marches out of the hospital wing, followed by Fudge.
Harry and Hermione see Snape charge out of the castle doors, and run towards the Whomping Willow. He stops at the base of the tree, and looks around, before picking up the Invisibility Cloak. Snape seizes the branch that Lupin used to freeze the Whomping Willow, prods the knot, and enters the passageway.
Snape talks to Cornelius Fudge about the events in the Shrieking Shack as they walk along the corridor together after leaving the hospital wing. He asks Fudge whether the Dementors' Kiss will be performed immediately, and smirks when he hears that it will be done as soon as the Dementors arrive.
When he discovers that Sirius has escaped, Snape furiously bursts in to the hospital wing followed by Fudge and Dumbledore. He is certain that Harry and Hermione had something to do with his disappearance, and bellows at Harry to tell him what they did. He sounds almost hysterical as he tries to persuade Fudge that he is right. He stands, seething, during Dumbledore's defence of the pair, then storms out of the ward.
As Dumbledore manages to convince Fudge that Lupin was trying to save the lives of Harry, Ron and Hermione, Snape is denied the possibility of being awarded the Order of Merlin. Lupin thinks that this is the last straw for Snape. The next morning, Snape tells the Slytherins that Lupin is a werewolf, and that he was roaming the school grounds the night before.
Professor Snape appears to have attained new levels of vindictiveness over the summer, and is in a foul mood. The students attribute this to his failure once again to get the Defence Against the Dark Arts position. Snape appears strangely wary of showing his animosity to Mad-Eye Moody, and gives the distinct impression that he is avoiding Moody's eye, whether magical or normal.
Professor Snape forces the fourth-year students to spend a lot of time researching antidotes for their homework. He hints that he might poison one of the students before Christmas to check whether their antidote works.
Professor Snape arrives at the dungeons after Draco and Harry have attempted to duel. He asks Malfoy to explain the scene in a deadly soft voice; he is cruel when he tells Hermione he sees no difference in her appearance, despite the fact her front teeth have grown down past her collar and he sends Goyle to the hospital wing. Snape deducts points from Gryffindor and gives Ron and Harry a detention each for their role, but does not punish the Slytherin participants.