Milestones in Abstract Thought

Our son's first known simile was observed a month or two ago. It's raining today, and he said it again. Although it's not exactly pleasant, it seems like it's something we should record:
He: "Rain is like poopie coming out of the sky."
We: "How is it like poopie coming out of the sky?"
He: "It just kinda is. It's just kinda like that."