It was the very beginning of the term and a dark haired Professor with an enormous beard was leading a group of nervous first years to the front of the Hall. The sorting ceremony proceeded as usual until the Professor called, "McGonagall Minerva."
A small girl with a pale face and dark hair stepped nervously forward and clambered upon the stool, whereupon the sorting hat was placed on her head. At the staff table a thin, elderly witch leaned across to a much younger Albus Dumbledore and whispered, "Another McGonagall, Slytherin, like every other in the last three centuries."
"SLYTHERIN!" exclaimed the sorting hat, apparently agreeing with the elderly witch. However, as the hat was removed from the girl's head something happened that had never before occurred in the history of Hogwarts and has not occurred since either.
"WAIT" called the hat.
The dark haired Professor with the enormous beard, the Deputy Headmaster and Head of Ravenclaw froze with the hat in his hands, as everyone in the room stared in amazement. Slowly, he lowered the hat back onto the girl's head and it began to mutter to itself.
"Slytherin you are through and through, descendant of Slytherin students, Slytherin blood in your veins, a Slytherin heart and a determined Slytherin mind. Slytherin you should be. And yet, there is something, something I can barely see, but it could make all the difference in the world to who you are and who you will be. I wonder now, what choice you will make, whether you truly have a heart of more than a self-seeking Slytherin." The hat paused in its thoughts. "Since I see everything ends with a choice, maybe I should let you make your choice now…do you want to go to Slytherin, the house of your forefathers?"
The girl on the stool thought deeply for a moment and the reply formed in her head. "My family want me to…how can I refuse?"
"They would never know," the hat reassured her, "They would believe I chose," he paused, "Never before have I allowed a student to choose their own fate."
"Then no," she thought, "I do not wish to be Slytherin, I know what my family are, and I wish to try a different path."
"Very well," the hat murmured, "I CHANGE MY MIND…GRYFFINDOR!"
A shocked, frozen silence greeted this announcement. There was no cheer from the Gryffindor table and the Deputy Headmaster made no move to remove the hat. The sorting hat had never before and would never again change its mind after making an announcement.
"Should I go now?" the girl thought to the hat.
"Yes," the hat replied, "I will not sort you a third time."
A small smile played with her lips and she got to her feet, carefully placing the hat on the table before walking over to the Gryffindor table. As she approached the table still no one made a sound, or even moved. Then, all of a sudden Professor Dumbledore, Head of Gryffindor House, stood at the staff table and clapped his hands proudly for his new student. The spell on the hall was broken and the Gryffindor table quickly joined in, applauding and even managing a modest cheer.