People have the misconception that because trees are stationary and slow, they are peaceful and gentle. People would also like to believe that carnivores are the most violent beings in the world. But the truth is that carnivores are the least violent beings in the world.
The most violent beings are herbivores and plants. Without carnivores, herbivores will massacre most of the plant life in a region. This and the fact that carnivores don't eat plants make plants like them.
Plants are also violent because every moment of their lives, they are always struggling for survival and spent fighting one thing or another for resources. If they fall behind in the struggle, they will die.
The worst part of their existence is that they can hardly defend themselves against herbivores. They can only stand there and let themselves be eaten.
So Arthur wasn't surprised that the tree had so much to say about violence and killing things. He tuned out all the talk of violence and made his request.
