Now we get a digression on intelligent species on Earth. See, humans thought they were smarter than dolphins because humans built stuff, like guns and cities, whereas all dolphins did was play around in the water.
Of course, the dolphins thought they were smarter for that same reason.
Also, the dolphins knew about the destruction of Earth and left before the Vogons came. They did try to warn people, but no one realized what they were saying. So the dolphins gave one last message and left.
The message: "So long and thanks for all the fish" (3).
But there was another species on Earth even more intelligent than humans and dolphins—a species that spent most of its time running on plastic wheels and running mazes in labs.