In their first year, Harry had once "defeated" a troll together with Hermione, Ron, and Neville.
That defeat had been rather unusual, because the four youngsters had not actually known any decent combat magic at the time. If they had fought it head-on, getting concussions from the troll's club would probably have been the best outcome.
The more likely outcome would have been getting turned straight into mincemeat.
By the end of their first year, though, the four had been confident that if they tried again, fighting four against one, they would have had at least a fifty-fifty chance of winning.
As for now, Harry felt he could at least keep himself safe against a troll on his own.
Even so, Harry still found it very hard to accept the small group of trolls standing in the corridor outside the Gryffindor Common Room.
There were many kinds of trolls, too.
For instance, the one Harry and the others had fought in the basement was the largest kind, but also the stupidest.
The kind in the corridor now was very closely related to that kind, yet the actual difference between them was hardly any smaller than the difference between humans and chimpanzees.
These trolls were only about two meters tall, knew to wear clothes, and had gray-green skin. They lacked the layer of rocklike skin covering those larger trolls, but their skin was tough as well.
Harry had read about them in a book. These were forest trolls, and they were fairly intelligent. The larger but rather stupid kind were hill trolls, the largest of which were called mountain trolls.
But trolls were still trolls. Bringing a whole group of trolls into a school for wizards really was rather hard to accept.
Still, there was nothing to be done about it.