Nothing happened. Harry clenched his hands to stop them from shaking. 

"Show yourself!" Snape said, tapping the map sharply. 

It stayed blank. Harry was taking deep, calming breaths. 

"Professor Severus Snape, master of this school, commands you to yield the information you conceal!" Snape said, hitting the map with his wand. 

As though an invisible hand were writing upon it, words appeared on the smooth surface of the map. 

Mooney presents his compliments to Professor Snape, and begs him to keep his abnormally large nose out of other people's business." 

Snape froze. Harry stared, dumbstruck, at the message. But the map didn't stop there. More writing was appearing beneath the first. 

"Mr. Prongs agrees with Mr. Moony and would like to add that Professor Snape is an ugle git." 

It would have been very funny if the situation hadn't been so serious. And there was more.... 

"Mr. Padfoot would like to register his astonishment that an idiot like that ever became a professor." 

Harry closed his eyes in horror. When he'd opened them, the map had had its last word. 

"Mr. Wormtail bids Professor Snape good day, and advises him to wash his hair , the slimeball.

" Harry waited for the blow to fall. 

"So..." said Snape softly. "We'll see about this...."

 He strode across to his fire, seized a fistful of glittering powder from a jar on the fireplace, and threw it into the flames.