I think the author was trying to tell us that our lives are a succession of hardships and fortune.
One day, the main character of this movie noticed a huge creature was approaching her(I can't say exactly the character is male or female...) when she woke up. She was trying to fight, but her power was so weak to beat it. She was swallowed and she thought there's no hope to get out of the creature's stomach, but fortunately, she was able to. She was relieved when the the hardship was gone, but at the same time, she noticed that a new creature was coming to her again and this would be continued forever.
I think what the author wanted to teach us is this: even if you are lucky or happy, you shouldn't be quite proud of it, and even if you are in trouble, you don't have to take it so serious, because you can go through it surely.
