Fear

Fred and George Weasley could do nothing but stare. There were no words shared between them and no witty remarks as to what they were seeing. Eventually, people started walking by them and stopped to look at what could possibly have the two loudest students at Hogwarts so dumbstruck. They stopped and starred as well.

Eventually there became a gathering of students so large that the teachers had begun to pay attention to the group. It did not take long for Professors McGonagall and Snape to reach the front of the group, ready to reprimand the gatherers of the crowd. But what they saw when they looked at the focus of attention made them stare as well.

After a few moments of staring, Professor McGonagall managed to ask, "What… What is that man doing?"

Fred Weasley answered in almost broken tones, "Wanted… Bogart… Dementor… know what fear… fears"

As the context to the strange sight before the crowd reached the back, the people of Hogwarts looked on in shock as something happened that had never happened in recorded history.

A Dementor Screamed.

The figure that made it scream stood calmly and turned to the crowd. The Bogart, for that is what it was, did not shift forms to match any other person's fears as many expected, but it did walk up to Professor McGonagall. It held out its hand to be shaken and said in a pleasant sort of voice, "Hi there. Xander Harris, I'm here to take care of the Dm'tor Demon infestation you have."

With that he pulled an ax from his back and walked in the direction of the nearest Dementor.