It was December, and it was freezing cold in the Potions dungeon, but Snape didn´t care. "Can anyone tell me what this is?" he demanded, holding up a transparent phial of steaming green liquid and surveying the class critically. "Longbottom?"

Neville, who had been trying in vain to warm his blue-tipped fingers over his cauldron, looked horrified. "I don´t know, Professor."

"Did you not complete your reading last night, Longbottom? The assignment was ten pages in the Lieber and Stoller book."

"I know, Professor, but my toad, Trevor, went missing, and I-"

"Ten points from Gryffindor!" barked Snape, who was in fine form. He didn´t even look cold, Draco mused. Perhaps he´d mixed himself up a Warming Potion before class.

Snapeś ink-black eyes darted over the students. "Potter?´ he inquired.

Out of the corner of his eye, Draco saw Harry pale and look startled. Next to him, Hermione went red. Every time she knew an answer and Harry didn´t, Draco had the feeling that she might actually implode with the effort of trying to will the knowledge in Harryś direction.

Itś an Imperceptus Potion, Draco thought lazily at Harry. Makes you invisible. Harry sat up straight. "An Imperceptus Potion," he said. "It makes the drinker invisible." Snape looked disappointed. "And the ingredients?" he snapped. Mugwort, Draco thought. Crushed dragon bone, powdered aspś blood, tansy, peppermint… "Mugwort," said Harry.

"Crushed dragon bone, powdered aspś blood, tansy, peppermint…"

And a pair of my very own boxer shorts, the ones with the little Snitches on them, Draco added.

"And a pair of…" Harry began, and choked. His face went red and then white as he succumbed to a prolonged coughing fit. Hermione gazed at him in alarm. Draco looked innocently at his quill, twirling it in his fingers.