Harry did not ask how Dumbledore knew

Harry did not ask how Dumbledore knew. He had never seen a wizard work things out like this, simply by looking and touching; but Harry had long since learned that bangs

and smoke were more often the marks of ineptitude than expertise.

Dumbledore stepped back from the cave wall and pointed his wand at the rock. For a moment, an arched outline appeared there, blazing white as though there was a

powerful light behind the crack.

“You've d-done it!” said Harry through chattering teeth, but before the words had left his lips the outline had gone, leaving the rock as bare and solid as ever.

Dumbledore looked around.

“Harry, I'm so sorry, I forgot,” he said; he now pointed his wand at Harry and at once, Harry's clothes were as warm and dry as if they had been hanging in front of a

blazing fire.

“Thank you,” said Harry gratefully, but Dumbledore had already turned his attention back to the solid cave wall. He did not try any more magic, but simply stood there

staring at it intently, as though something extremely interesting was written on it. Harry stayed quite still; he did not want to break Dumbledore's concentration.

Then, after two solid minutes, Dumbledore said quietly, “Oh, surely not. So crude.”

“What is it, Professor?”

“I rather think,” said Dumbledore, putting his uninjured hand inside his robes and drawing out a short silver knife of the kind Harry used to chop potion ingredients,

“that we are required to make payment to pass.”

“Payment?” said Harry. “You've got to give the door something?”

“Yes,” said Dumbledore. “Blood, if I am not much mistaken.”

“Blood?”

“I said it was crude,” said Dumbledore, who sounded disdainful, even disappointed, as though Voldemort had fallen short of higher standards Dumbledore expected. “The

idea, as I am sure you will have gathered, is that your enemy must weaken him- or herself to enter. Once again, Lord Voldemort fails to grasp that there are much more

terrible things than physical injury.”

“Yeah, but still, if you can avoid it...” said Harry, who had experienced enough pain not to be keen for more.

“Sometimes, however, it is unavoidable,” said Dumbledore, shaking back the sleeve of his robes and exposing the forearm of his injured hand.

“Professor!” protested Harry, hurrying forward as Dumbledore raised his knife. “I'll do it, I'm —”

He did not know what he was going to say—younger, fitter? But Dumbledore merely smiled. There was a flash of silver, and a spurt of scarlet; the rock face was peppered

with dark, glistening drops.