Remus Lupin had been very young when he’d been bitten. So young that now he couldn’t remember a time in his life when he hadn’t been affected. How had he first learned that he was doomed forever to suffer the monthly transformation? He couldn’t even recall. It seemed as if it had always been a part of him. A terrible part, of course. An unstoppable, impossible to hide, hideous part from which he suffered so continuously.
He remembered being very young - around five years old - and sobbing against his father’s chest the morning after. “Why?” he’d asked plaintively. “Why, Dad?” His father had no answer but had simply held him, stroking his hair quietly.
It was much the same two years later when he was a somber child of seven. He hadn't wanted to go into the garden shed, and he'd cried and thrown a tantrum. His mother was crying, too, he’d noticed. It sounded as if her heart were breaking. Remus’ father had grabbed him roughly, dragging him into the shed, anger flashing in his gray eyes. But then his father had sat with him in the shed for a little while, his arm wrapped around him comfortingly. “Son, this hurts your mother and me so much. We don’t have any choice. We have to protect you. Please don’t make it more difficult than it has to be.” Remus obediently went into the shed after that. He always felt so alone - locked up, waiting for the moon to rise and for it to happen. Completely and utterly alone he waited to feel the call of the moon begin its torturous transformation of his body.
The transformation was always the same. First his bones started to change shape. Tears coursed down his cheeks and he screamed in pain as his body involuntarily hunched into its lupine form, bones shifting, expanding, and contracting. Skin and muscle stretched and tore over his changing skeletal shape.
Great claws ripped horribly through the flesh of shriveling fingers. New teeth grew in, large and sharp, tearing through soft gums as his face and jaw elongated excruciatingly. Tufts of fur quickly sprouted over his body with the crazy, stinging feeling of a million biting ants.
Once the pain of his physical transformation began to dissipate, Remus could feel the wolf’s senses becoming alert. He could smell the night. The scent trail of the neighbor’s dog flickered past his now so sensitive nose, enticing him. The rabbit that had hopped past had left its fragrance, which wafted luxuriously around the small confines of the shed. Most intriguing of all was the human scent, which was everywhere. The human odor drew him like no other. It was tantalizing, and inviting - almost sensuous. It triggered in him a mad impulse to hunt. He wanted, no not wanted, needed, he needed to rip, tear, and bite. If it were not for the stout wooden shed and ironclad door, Remus knew the wolf would be unstoppable in its hunt for this particular prey.
The thoughts in Remus’ brain grew muddled and confused as the wolf took over. Instinct overtook intellect, animal desires overtook reason. The being that was Remus was going away and left in his place was a mad, frantic, destroyer whose basest craving was to hunt.
When Remus felt his consciousness leaving his body, he knew it was sign of his final and utter descent into the wolf. To Remus, this was the most painful effect of his transformation.