In Yggdrasil, the great tree that holds up the entire world, there lived a squirrel called Ratatoskr. He was small and red and fast as lightning, and his tail was almost as big as himself.
Ratatoskr had the most important job in the whole tree. He was a messenger. Every day he ran up and down through the trunk, from the deepest roots to the highest branches and back again.
At the very top of the tree lived an enormous eagle. No one really knew his name, but he was very old and very wise, and his eyes could see all the way to the edge of the world. Between the eagle's eyes sat a little hawk called Veðrfölnir, and he kept watch for the eagle day and night.
Far down at the roots lived the dragon Níðhöggr. He was dark and old-fashioned and grumpy, and he chewed on the tree's roots all day long. Gnaw, gnaw, gnaw. He had been doing it for so long that no one remembered when he started.
The eagle and Níðhöggr did not like each other. They had never actually met, because the eagle always sat at the top and Níðhöggr always lay at the roots, but they had very firm opinions about each other all the same.
And that was Ratatoskr's fault.
Every morning Ratatoskr climbed up to the eagle. "Níðhöggr thinks you sit too much," he said. "He says you just stare and never do anything useful." The eagle ruffled his feathers and grumbled. "Tell that old worm that I can see everything from up here. I can see him lying down there chewing like a rodent." Ratatoskr nodded eagerly and dashed downward.
"The eagle thinks you chew too much," he said to Níðhöggr. "He called you a rodent." Níðhöggr snorted and a little puff of smoke rose from his nostrils. "Tell that vain feather-ball that without my roots he would have nothing to sit in." Ratatoskr nodded eagerly and dashed upward.
And so he went on. All day, every day. And if you listened very carefully you could hear that Ratatoskr sometimes added a little extra. If the eagle said Níðhöggr was old, Ratatoskr told Níðhöggr that the eagle had called him ancient and toothless. If Níðhöggr said the eagle was vain, Ratatoskr told the eagle that Níðhöggr had called him the most puffed-up bird in all nine worlds.
Why did Ratatoskr do it? Perhaps he thought it was fun. Perhaps he believed it was his duty. Or perhaps he knew something the other two never understood: that as long as the eagle and the dragon quarrelled with each other through him, they stayed busy, and as long as they stayed busy, the tree kept standing.
Ratatoskr ran and ran. Up and down. Down and up. His little claws clicked against the bark and his great tail waved behind him like a flag, and he smiled the whole time, because Ratatoskr was the happiest creature in all of Yggdrasil.
And they say he is running still.