Automatic Drawing: Troll with holy stone

A few days ago I made some automatic drawings on a train journey. I said I would scan them when I got home. Well, I'm home, and here is the first one, a troll examining a 'holy stone', which is to say a stone with a hole that runs all the way through it. In folk magic these are said to trap evil spirits. Trolls seem quite fond of them. Whether for the same reason I cannot say.