One of the first things Gareth figured out about dogs is that, in Doggish, woof and arf are the same thing, and each one means whatever the dog in question happens to be thinking when he says it. Nonetheless, Woof Woof is always on Mars, and Arf is always in Fairyland. Both can now be reached by pretending to drive my car, but they're very far apart, and Gareth scorns the idea that I could be confused about which one we've arrived at. They're nothing alike, Mars and Fairyland! Surely Mommy knows that!
It's not yet clear who lives in Arf. Fairies, presumably, and there are probably dogs, too. However, I am assured that there are no robots in Arf, though robots are quite common in Woof Woof.
My two-year-old knows there's a difference between science fiction and fantasy, and it's a boundary he cares about policing. How did he figure that out?