“It’s not a case of what you’ll permit, Minerva McGonagall. Your time’s over. It’s us what’s in charge here now, and you’ll back me up or you’ll pay the price.”

And he spat in her face. 

Harry pulled the Cloak off himself, raised his wand, and said, “You shouldn’t have done that.”
As Amycus spun around, Harry shouted, “Crucio!”

The Death Eater was lifted from his feet. He writhed through the air like a drowning man, thrashing and howling in pain, and then, with a crunch and a shattering of glass, he smashed into the front of a bookcase and crumpled, insensible, to the floor. 

“I see what Bellatrix meant,” said Harry, the blood thundering through his brain, “you really need to mean it.”

“Potter!” whispered Professor McGonagall, clutching her heart. “Potter — you’re here! What — ? How — ?” She struggled to pull herself together. “Potter, that was foolish!”

“He spat at you,” said Harry. 

“Potter, I — that was very — very gallant of you — but don’t you realize — ?”

“Yeah, I do,” Harry assured her. Somehow her panic steadied him. “Professor McGonagall, Voldemort’s on the way.”

“Oh, are we allowed to say the name now?” asked Luna with an air of interest, pulling off the Invisibility Cloak. This appearance of a second outlaw seemed to overwhelm Professor McGonagall, who staggered backward into a nearby chair, clutching at the neck of her old tartan dressing gown. 

Harry Potter and the Deathly Hallows – J.K. Rowling