Disappointment in Dumbledore's Voice

There was a knock on the office door and Snape, now looking happier than ever, opened it. There stood the Headmaster, Professor Dumbledore.
Harry's whole body went numb. Dumbledore was looking unusually grave. He stared down his very crooked nose at them and Harry suddenly found himself wishing he and Ron were still being beaten up by the Whomping Willow.
There was a long silence. Then Dumbledore said, 'Please explain why you did this.'
It would have been better if he had shouted. Harry hated the disappointment in his voice. For some reason, he was unable to look Dumbledore in the eyes, and spoke instead to his knees.

THE WHOMPING WILLOW - Pg 84