Trolls in my attic

The trolls in my attic are constantly scampering around. They are the noisiest bunch of trolls, and there must be at least fifty of those little buggers up there. Many people have asked me why I allow trolls to live in my attic, but they just refuse to leave.

One sunny day, I decided to go into the attic and open the window to air it out. A couple of days later, I started to hear strange sounds up there. I opened the attic door and found the trolls. "Why are you here?" I shouted. One of the trolls, the Great Troll Zolan, replied, "Squirrels have infested our tree, and we saw your window was open. That was an invitation to come in."