"Lupin!" Snape called into the fire. "I want a word!"

 Utterly bewildered, Harry stared at the fire. A large shape had appeared in it, revolving very fast. Seconds later, Professor Lupin was clambering out of the fireplace, brushing ash off his shabby robes. 

"You called, Severus?" said Lupin mildly. 

"I certainly did," said Snape, his face contorted with fury as he strode back to his desk. "I have just asked Potter to empty his pockets. He was carrying this." 

Snape pointed at the parchment, on which the words of Messrs. Moony, Wormtail, Padfoot, and Prongs were still shining. An odd, closed expression appeared on Lupin's face. 

"Well?" said Snape.

 Lupin continued to stare at the map. Harry had the impression that Lupin was doing some very quick thinking. 

"Well?" said Snape again. "This parchment is plainly full of Dark Magic. This is supposed to be your area of expertise, Lupin. Where do you imagine Potter got such a thing?" 

Lupin looked up and, by the merest half-glance in Harry's direction, warned him not to interrupt. 

"Full of Dark Magic?" he repeated mildly. "Do you really think so, Severus? It looks to me as though it is merely a piece of parchment that insults anybody who reads it. Childish, but surely not dangerous? I imagine Harry got it from a joke shop --" 

"Indeed?" said Snape. His jaw had gone rigid with anger. "You think a joke shop could supply him with such a thing? You don't think it more likely that he got it directly from the manufacturers?" 

Harry didn't understand what Snape was talking about. Nor, apparently, did Lupin.