Children's books are obsessed with butterflies. Like, super obsessed. We can't say for certain why, but we've got two guesses: First, they're pretty; second, we admire their ability to transform. If I Ran the Zoo is surprisingly lacking in butterflies, but the transformation part of any good butterfly story remains.
McGrew's imaginative journey is a matter of mental transformation. He assumes the clothes of the zookeeper, changing himself into a zookeeper for the duration of his daydream. As the zookeeper, he gets to be a different person, do something different with his life. We might not have the physical transformative powers of the butterfly, but, according to Seuss, our imagination will do in a pinch.
Q: Why does McGrew imagine owning his own zoo?
A: Maybe he just wanted to see what it would be like to own a zoo for a day. And if you're going to own a zoo for a day, you might as well make it the best zoo ever.
Q: Why does he get rid of all the lions and bears?
A: He doesn't really get rid of them. Remember, he had a ten-legged lion (5.2)? It's more like he's transforming them into something more fitting for his own world.
Q: Do you think I could change like McGrew?
A: Sure, anyone can if they have the imagination and gumption.