Farnsworth: It's a sunny little doomed planet, inhabited by a number of frisky little doomed animals.
Leela: Animals?
Farnsworth: That's right. Animals in desperate need of rescue. You see, Vergon 6 was once filled with a super-dense substance known as dark matter, each pound of which weighs over ten thousand pounds.
Leela: Wait! What about the animals?
Farnsworth: Well, dark matter is extremely valuable as starship fuel. That's why it was all mined out, leaving the planet completely hollow.
Leela: Yes, but what about the animals?
Farnsworth: The wha'?
Leela: The animals.
Farnsworth: I didn't say anything about animals. Now it seems that the planet will collapse within three days. Incidentally, this will kill all the animals.