But What If…

And that ties into what this story is really about: the fear of making the wrong choice (source). The kids in the story haven't even seen a lot of the animals they mention in the story, and many of them probably don't exist. But there's this idea of the perfect pet that they're always chasing. Sure, this dog is pretty great, but what if there was an animal that could fly around on a string?

The time may be now
to make up my mind.
But who knows what other
good pets I might find?

I might find a new one.
A fast kind of thing
who would fly round my head
in a ring on a string! (20.1-21.4)

The narrator knows he has to make up his mind, but he can't help but entertain the "what if" questions. With so many options, both real and imagined, he struggles to make the "right" choice.