Symbolism, Imagery, Allegory
The gastropodarium is a little world within a world. It's the world Shin created for his pods, and he rules it. This whole metaphor is pretty well spelled out and explored by Shin himself:
"They look up and I am this great shadowy figure—pods don't see much beyond light and dark. I am like a cloud that comes and goes. I provide their food and water. I control the temperature, the light, everything. I am the Pod God." (4.66)
That's a pretty tidy metaphor, right? But Shin becomes so obsessed with the Ten-legged God that he neglects his pods—their pond dries up and the gastropodarium gives off such a stink that Jason thinks its inhabitants are all dead. Shin explains that they are estivating (see Shin's analysis in the "Characters" section for more on this). He tells Jason, "'I've been busy'" (16.24). And though Jason has spent plenty of time being generally mortified by his nerdy friend, he feels "bad for the snails. Shin is their god, and he has abandoned them" (16.36).
And that there is a problem that people have wrestled with for millennia: If there is a god out there, is she/he/it active in our world and in our lives? Does god care? What does it mean when god feels absent? Hold up… those sound like some of the key questions that are grappled with in this book.
Toward the end of the book, after everyone is done climbing the tower and Shin's spent time in the mental health ward of the hospital, Jason notices that the gastropodarium is no longer in Shin's room. Shin explains, "'I let them all go. I let my pods go'" (30.62). (Notice that the sentence construction echoes Moses's escalating demands that Pharaoh "let my people go" in Exodus. Cool trick, right?)
Why do you think Shin lets his pods go?