This story was interesting for me.
I suppose the thing is the symbol of human's heart.What I felt when first I saw the boy in this story is that he looked a little sad, his heart was not so warm and he hadn't been able to find the place in which he could be relieved. I think the thing stands for his unstable mind. It was like a robot and might be made by iron so it is contrary to humans or human's heart. Since they met at the beach for the first time, they seemed to have especilly no change for a while.But after that, the boy put some colorful flowers into the thing and I think it meant that the thing gained kind of warm heart like humans. Then, it found the place to which it should go back and said good-bye to him. I think through this experience, he learned that the heart is necessary for humans. It shouldn't be empty but be filled with warmth to some extent. It may lead people to find their own place they can be relieved in. I don't know if he could gain the warm heart, but the thing might have him grow up than before.
