This is a very interesting film.
The leading character recollects old days when he was wandering with a strange creature which probably came from garbage and was thinking about whether things around him were able to use or not.
At the end of the story,the boy and the creature entered a vivid and beautiful world in which things,especially used things were moving vividly and very freely.From this part, what the film has to say is that every things have minds and they want people to use them until the things are not able to be used any more,as Minori said.Of course,the producer considered the fact that when things get to be a little older,we refrain from using them or even throw them into garbage bins.This movie features modern cities not particular cities.Deduction of senses of things around us becomes a price for the fact that cities become modern and rich .
Finally,I think lost thing is in our heart not in the visible world,that is,lost thing is not entity.
