We have an anatomy book in which the different systems are represented by different teams of tiny people working inside the body.
Brother-Bug: Mama, when those little guys are working inside the body, where do they go to the bathroom?
Mama-Bug: Sweetie, those little guys aren't really in your body. It's just imaginary in that book.
Brother-Bug: I KNOW it is imaginary. But where would they go to the bathroom...if we were imagining?
Mama-Bug: I suppose if there are imaginary people inside your body, they must have imaginary bathrooms.
And with their Grandmommie just back from holiday in Sicily, we were talking about volcanoes and Mount Etna today. A lot.
Brother-Bug: Mama! I think the inside of my nose is turning into a volcano!!
Mama-Bug: What might happen then!?
Brother-Bug: I will have hot lava snot! I might erupt!
Mama-Bug: Well, if that happens take it outside. I don't want volcanic ash all over my living room.
Brother-Bug: Maybe I can erupt by the mail box?