Snow was swirling against the frost covered windows. After strolling around the classroom in order to check if everything was ready for the upcoming lesson, Ambrosius stopped near one of them. With a flick of his wand, he melted the ice so that he could observe the landscape while awaiting the arrival of his students. Seeing his own reflection in the glass, he noticed that his face was paler than usual, making the shadows under his eyes all the more visible and terrifying. He ran his long and thin fingers down his cheeks, as to check if the man he was seeing was really himself. The contact of his hand on his cold skin triggered a strain of memories from a time long gone. In his head, the pictures followed one another: he saw the dark hair and radiant smile of the young woman who had been haunting his thoughts, and remembered her gentle touch as if they had never parted. However, he knew where this reminiscence would inevitably lead him, and he always tried to avoid adventuring into that painful place. On the window, a drop of water ran down the reflection of his cheek.

Suddenly, the door of the classroom opened, snapping Ambrosius out of his thoughts. Still a little shaken, he walked to his desk and stood behind it while the students were entering in small groups. “Good afternoon, everyone.” he greeted them with his usual calm voice. “I hope you enjoyed yourselves during the holidays. However, as you have surely noticed, they are now over and I therefore expect nothing less than your full attention and hard work.” He marked a brief pause, his gaze going from face to face to make sure the message was clear. Leaving his desk, he started wandering around the room, his hands behind his back, as he pursued: “As you may remember, before the break we learned the first of a set of defensive spells that I am going to teach you this year. Can anyone tell me what charm it was?" he asked, to make sure that the students hadn't forgotten everything, as it was sometimes the case after a long break.

Keith Parker raised his hand. "Would it be the Knockback Jinx?" He asked quietly, in hope that he had answered it correctly, as he didn't want to make a fool of himself in front of the whole class. He didn't bother to look at the other students, to see their expressions, he kept his focus at Professor Umbranox.

Kim entered the room, observing if there are any new decorations. Though nothing is arranged in a different way in their lesson for today, the professor's paler appearance caught her attention. He looks like ill, though his voice is perfectly authoritative, indicating nothing is wrong. After some curious thoughts passing by, he began to have the introduction.

Hearing some words of advices, he said, “As you may remember, before the break we learned the first of a set of defensive spells that I am going to teach you this year. Can anyone tell me what charm it was?" A gryffindor guy immediately raised his hand. "Would it be the Knockback Jinx?" He asked quietly. Kim looked back at the professor, waiting for a response.

James ran through the corridor leading to classroom 3C. He was almost late for once, even if it wasn't entirely his fault. He had indeed crossed paths with Peeves, the poltergeist who was roaming the Castle continuously looking for ways to put the students into trouble. This time, he was throwing water balloons at students who were passing through one of the corridors on the fourth floor. James, having seen the mayhem that was awaiting him, decided to take a detour in order to avoid it. However, since he still didn't know the Castle that well, he got lost after a series of moving stairs and long hallways, since he still didn't know the Castle that well and had never been very skillful when it came to orientation. Finally, after what seemed an hour of fruitless wandering, he nearly jumped from happiness when he perceived the familiar Defence Against the Dark Arts classroom.

Entering the room, he promptly headed towards his usual seat, grabbed his book from his bag and placed on the desk in front of him. He glanced at the blackboard for indications on the subject of the lesson, but it was blank. After a few minutes, Professor Umbranox started the lesson, pointing out that the fun they had during the holidays was now over and that some serious work was expecting them.

Richard turned the corner and walked down the hallway. In front of the Defence Against the Dark Arts classroom, he noticed James, who was trying to catch his breath before entering. He approached, wanting to ask his classmate if everything was all right, but the latter pushed the door before Richard could get to him. He slipped into the opening, and once in the room, silently walked to the place next to Kim. "Hi, Kim" he greeted her as he was taking his seat.

After everyone was set, Professor Umbranox began his introductory speech. As he was talking, Richard couldn't help but notice that he looked even more frightening than usual. His face was paler than ever and he seemed troubled or even sick. After a few minutes, one of his classmates raised his hand after the teacher asked if anyone remembered the subject of last lesson. Always trying to gain the professor's favours and receive some points, Richard thought, looking at the Gryffindor boy with some contempt. However, he had more important matters on his mind. "Hey, don't you think that Professor Umbranox looks kind of strange today?" he whispered to Kim, taking advantage of the fact that the Gryffindor was answering to cover the sound of his own voice. "I mean, more than he usually is." he precised, looking at her.

Bill entered the room and look out to the students and finally a professor. He looked paler than he was when Bill last saw him, strange that this would happen maybe he was sick. Bill searched for the open place and found it near James, guy from Ravenclaw that he knew. Bill went and sat there as James opened his book and start to read, so typical behavior for him he always read something. "Hi James how was your holidays?" Bill asked him but professor interrupted them. He asked what was that they learned last semester and before Bill could raise his arm to answer, other guy from Gryffindor answered professors question. Bill sat there waiting for the continuation of the lesson.

As Keith waited for an answer from Professor Umbranox, he noticed that he looked a little different, or maybe it was just him. Keith couldn't shrug the thought off, though, and continued wondering if Professor Umbranox might have been ill or he maybe just hadn't gotten enough sleep. Deciding it was none of his business, he looked around the classroom at the other students, who also seemed to have noticed Professor Umbranox's looks.

"Would it be the Knockback Jinx?" Keith Parker answered. "Very good, mister Parker. I am glad to see at at least some of you still remember what we did until now. Since we have seen every aspect of the Knock-Back Jinx, I believe that we can move on to the next spell. If you do not have any questions, that is." He waited several seconds, but none of his students raised their hand. He pursued, though he noticed that they were all observing him with consistence. "As we have seen last time, the Knock-Back Jinx has a certain number of limits which make him ineffective in some situations. Therefore, we are going to learn today two new defensive charms that may prove very useful for all of you in the future."

Approaching his desk, he took out his wand and swiftly flicked it. A piece of chalk flew out of his bag, levitated towards the blackboard, and then stopped at a few inches from the surface, hovering in mid-air, waiting for further instructions. Ambrosius faced his audience and announced: "The subject of today's lesson are the Petrificus Totalus and the Immobulus spells." While the students were pulling out their quills and parchments in order to take notes, one could hear the grating sound of the chalk writing on the board. "Since I hadn't given you any homework during the holidays, you may still be unacquainted with these charms. Unlike the other lessons, there will therefore be two parts in this lessons. First, we will be learning about the theory concerning these spells and after that you will have the opportunity to practice them in groups as usually."

Ambrosius ceased his stroll between around the classroom and turned towards his audience. "We will start with Petrificus Totalus. Has anyone heard of this curse before or has an idea, however vague it may be, concerning its effects?" he asked, his gaze moving from student to student.

Keith remembered seeing two fifth years practicing the spell on each other once. Keith raised his hand again. "Petrificus Totalus is a spell that freezes or petrifies the body of the victim, making it incapable of moving, except for the eyes and the breathing." He answered, but glancing around the classroom, he realized the other students might be thinking of him as a know-it-all.

"Yes, that is correct." Ambrosius replied after listening to his student. "5 points will be added to Gryffindor for your answer." He then addressed the entire class. "The Full-Body Bind Curse, also known as the Body Freezing Curse, is indeed a spell that renders the victim completely immobile. The incantation is Petrificus Totalus and the wand movement required to perform the spell is, from left to right, a hook, then a horizontal line and finally a short vertical line downwards." he explained while showing the motion with his wand. Behind him, the blackboard was filling with information about the spell.

"More precisely, the body of one hit by this curse will become rigid, making him or her fall on the ground due to a lack of balance. However, he or she will not be unconscious, and the spell does not affect his or her breathing ability. Furthermore, the victim is completely aware of what is happening around it being able to move its eyes, even if he or she cannot control any other part of the body. Therefore, the Full-Body Bind Curse is extremely useful in defence against dark forces, since if you succeed to hit your opponent with this spell, he or she will be unable to harm you in any way. Unlike the Leg-Locker Curse, which only blocks the victim's legs, it has the advantage of preventing a witch or wizard from using their wand, which is crucial when facing a dangerous opponent in battle.It goes without saying that the Body Freezing Charms is most effective on living foes, and it is mostly used when defending against witches or wizards. However, being more powerful than for example the Knock-Back Jinx, it is also more difficult to cast successfully, and requires a level of concentration that some of you might not achieve." Ambrosius explained.

He made a pause, listening to the scratch of quills on parchments as the students were writing down what he was saying. "Once someone is affected by the Body Freezing Curse, he or she cannot undo the effect of the spell by himself or herself whilst under it. However, there are several ways to "awaken" someone who has been hit by this curse. The first one is the Reviving Spell, whose incantation is Rennervate. Contrary to what its name indicates, it is not used to bring the deceased back to life, as that is impossible even in the wizarding world, however hard that may be to accept." he added with a shade of pain in his voice. "Its primary effect is to bring one back to consciousness after one has been afflicted by a Stunning Spell or a Full-Body Bind Curse. For those of you who are not familiar with it, the Stunning Spell is also a very useful weapon when defending against the Dark Arts, but as it requires a greater magical knowledge than you currently possess, you will only learn in further years. Another way to undo the result of Petrificus Totalus is to perform Finite or Finite Incatatem, which stop all currently remaining spell effects that it targets. The only difference is that the second aims at an area rather than a specific object or individual. Later, when you will be practicing the Body-Bind Curse, you will use the Reviving Charm as a counter-curse, since it is the easiest to perform of the three."

"As you may have noticed, Petrificus comes from the Latin petra, which means stone. You can also fin the same root in the word petrify: turn into stone. Even though the Full Body-Bind Curse may share some similarities with petrification, the two are fundamentally different. Does anyone know the distinction between them?" he asked, and then waited to see if one of his students had an idea.

Keith didn't seem to know this one. He looked around the classroom to see if any of the other students knew the answer to the question.

James was rapidly writing down everything the professor was saying, and regularly glanced at the blackboard to make sure he hadn't missed anything. After thoroughly explaining how the Full Body-Bind Curse worked, Professor Umbranox asked them about the difference between that spell and petrification. James knew nothing about this type of magic except what he had read in Muggle myths, but he was certain that it wouldn't be of much use here. He gazed around the room, thinking that maybe one of his classmates had the answer. He guessed that Keith, who he had practiced with during last lesson, may know it, since he seemed to be quite informed about the Body Freezing Charm, but the Gryffindor was also looking around. Maybe he just doesn't want to pass for a braggart James thought, a strategy he often adopted himself.

Kim, noticing that no one knows the answer, decided to break the silence. "Professor, I think that when the Full Body-Bind Curse is casted, the victim remains conscious, aware of what is happening around him or her. It is also possible for the caster to put some injury on the victim. On the other hand, when Petrification is used, the victim will stay unconscious and also, the caster can't put injuries on the victim, since technically, the victim already turned into a stone."

Hearing Kim's answer, a memory from Richard's childhood suddenly appeared in his mind. When he was younger, his mother used to tell him scary bedtime stories, much at his insistence. One of his favourite ones was the one about the Chamber of Secrets, a mysterious room located somewhere in the Castle, which had been opened several decades ago, releasing a monster that had the ability to petrify its victims. Remembering one of the details of the tale, he raised his hand and waited for Professor Umbranox to give him the permission to speak. "Also, as you said, the effects of the Petrificus Totalus Curse may be undone by a simple counter-spell, whereas it is much more difficult to "awake" someone who has been petrified. I think that a certain plant is necessary to do that." he explained, hopelessly trying to recall the name of the plant.

"Yes, these are the two main differences between the Full Body-Bind Curse and petrification. You will receive five points each for your correct answers" Ambrosius replied after the students had given their responses. "As you said, on one hand, petrification is very advanced Dark Magic and it cannot be countered by a simple spell, contrary to the Body Freezing Charm. On the other hand, when you have been petrified, you are completely unaware of what is happening around you, you slumber into some kind of deep coma until you are finally brought back to consciousness, whereas the Petrificus Totalus curse only results in the immobility of the victim's body. Another difference is that the effects of the Full Body-Bind spell are only temporary and will wear off after some time, even if no counter-curse is performed, whereas the ones resulting from petrification can last indefinitely, that is until the victim is administered a cure. The only known is obtained from a magical plant called Mandrake or Mandragora which, when matured, can be cut up to serve as a prime ingredient for the Mandrake Restorative Draught. a potion with the ability to awaken someone who has been petrified. I will not go into details now, as you will learn more about this fascinating plant in Herbology. Finally, there is also a major difference between the Full Body-Bind Curse and petrification in the way that they initially occur. Whereas the first is a rather elementary spell within the grasp of most wizards out witches, the second is Dark Magic of the most advanced kind. Although there are legends about dark wizards who were so powerful that they could turn someone into the stone, the only proven cause of petrification remains the gaze of the Basilisk, reflected in or seen through another object. As terrifying as this may sound, one of those snakes, also known as King of Serpents as they can reach gigantic size and live many hundreds of years, once dwelled in this very Castle."

He stopped for a moment, as several gasps could be heard throughout the classroom. "To get to the beginning of this tale, we have to go back over a thousand years, to the time of the creation of the School. As you know, Hogwarts was founded in the Middle Ages by four of the most brilliant witches and wizards of the time : Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw and Salazar Slytherin, who gave their names to the different Houses you have been sorted into." He started walking around the room, the students' gazes following him. "They all had their own opinion on who should be accepted to study at the School, and as three of them were able to co-exist quite harmoniously, one did not. Salazar Slytherin wished to be more selective in the choice of students. He believed that only Pure-Bloods should be permitted to attend Hogwarts, as he considered that Muggle-Born children didn't deserve to learn magic. Unable to convince the others of his elitist opinion, he left the school. However, before departing, he built a hidden chamber in the Castle, the Chamber of Secrets, and sealed it so that only his true heir would be able to reopen it. He or she alone will then have the ability to unleash and control the monster within the Chamber, and by doing so purge the school of all those who are according to his Slytherin's views, unworthy to study magic." He paused one more time, as a cold and tense atmosphere was descending upon the room.

"Of course, many searches were conducted to find the Chamber over time. None, however, were successful, and the Chamber of Secrets was dismissed as a mere legend by many. However, in 1942, a series of attacks on Muggle-Borns occurred, leading to the murder of one of them. Nevertheless, the supposed culprit was found, expelled and sent to Azkaban, the prison for wizards, even though the Chamber had still not been found. The case was considered closed, and for a long time there was no more talk of the mysterious chamber. Still, fifty years later, the attacks started again, along with messages that the Chamber of Secrets had been reopened. Luckily, this time, all the victims were merely petrified." He stopped, as many of the students were connecting this last piece of information with what he had told them earlier. "Yes, as you have certainly guessed, Slytherin's monster was a Basilisk, a beast whose gaze would instantly kill anyone who directly crossed it. However, this time, the victims only saw a reflection of the snake's eyes, hence being only petrified. After an escalating number of aggression, the school was on the verge of being closed. However, as everyone thought that all hope was gone, two wizards, in their second year at the time, found their way into the Chamber, defeated the Basilisk, and sent Slytherin's heir into oblivion, thus freeing the school from the threat of the Chamber of Secrets." Ambrosius glanced at the clock. Telling the story had taken him more time than he had planned.

"As much as I would love to tell you every detail about this fascinating tale, I'm afraid we have to move on with our defence spells. Besides, I believe that the story of the Chamber of Secrets is on your History of Magic curriculum, and you will therefore have the opportunity to discover every possible aspect of it." He paused for a moment, waiting to see if his students had any question about what he had just told them.