Everybody hissed and growled and squawked at this.

“Let me tell you a story about starlings!” the porcupine said. “Starlings originally came from Europe. That’s where they’re supposed to live. But then some nitwit got it into his head that North America should have every bird species mentioned in the works of Shakespeare.”

“Who’s Shakespeare?” the fishing cat asked.

“That is actually kind of a cool idea,” Kate said.

“No, it isn’t! It isn’t ‘cool’! It was a catastrophe! This nitwit released sixty European starlings in New York City, and they mated and bred, and now they’re all over America. There are two hundred million of them!”

“Okay, but what about those squirrels, though?” Kate said. “Little furry gray squirrels!”

“Oh, they went the other way round,” the porcupine said. “Gray squirrels are from America. But then a tourist brought a few home to England because he thought they’d look nice on his country estate. Nice! They have a high old time in England. They eat birds, they kill trees, and they’ve driven the native red squirrels practically to extinction.”

Kate thought about that. It didn’t seem like anybody involved had had such bad intentions, really. They were small gestures. She still thought the Shakespeare thing sounded cool. But then look at what had happened! Everything that was so neatly balanced was ruined. Couldn’t they send the animals back where they’d come from and start over? she wondered. More carefully this time? But how would you catch two hundred million starlings? She doubted she could even catch one.

Or a squirrel. There was no going back. The balance was lost forever.

She sighed. At any rate, she could keep them off her train.

“So what are all the other animals doing here?” she asked. “The ones who have tickets. How do you get tickets, anyway?”

“Oh, they just appear,” the heron said. “I found mine in my nest when I came back from hunting.”

“Mine was inside a fish,” said the cat. “I almost ate it.”

“My ticket was growing from a tree, like a leaf,” said the snake. “Whoever runs the trains must issue them. Or maybe the tickets just issue themselves.”

“But why?” Kate asked. “I mean, why do you need them? You’re not invaders, are you?”

“Course not.” Suddenly the heron sounded oddly embarrassed. “We’re just—you know. We’re migrating. That sort of thing. You know how we animals do that.”

Something about the silence that followed made Kate wonder if she was really getting the whole story. But the train was slowing down again.

“All right,” Kate said. “Excuse me, I think the train needs conducting.”