One day, on a lark, Erbert and Gerbert decided to go to one of Saturn’s moons, Titan, to see what it was like on the only moon in the solar system known to have an atmosphere. When they got there, they met Girf. Now Girf is not a normal boy’s name, but then again, Girf wasn’t really a normal boy. Because the surface of Titan is mostly frozen methane, Girf had mutated to develop long, sharp blade-like appendages that actually look like sled runners. So, wherever he went, he made the noise GRRRFFF, GRRRFFF and GRRRFFF—which sounds funny, but is serious business when you’re trying to get around a moon that’s coated with frozen methane. And so, once again, the boys learned an interesting lesson: Sometimes what seems like a weird mutation is actually a very clever adaptation.