Setting: A town near the beach. Long time ago
Conflict: The lost thing has nowhere to go. The boy tries to find where it belongs.
Climax: The boy finds the place where many other strange things live. The lost thing has gone there.
Symbol: train-real life, strange creatures-spare time(room, space)/useless(in a good way)/playfulness
Irony: The man no longer could see the creature after he sent off the lost thing
Theme: As we grew older, we tend to overlook something that were able to see before. We are sorting out what are profitable and what are useless/futile unconciously. I think what the film want to tell us is that there may be something very important although they are useless and you overlooked.
