"Ratatosk is the squirrel," Magnus says. He waits till Little John gets down the tree and clears the ladder before hopping lightly from the trunk to the cave below, landing easily on his feet -- it's not a high enough distance to bother him. "He's enormous, with claws like scimitars, and he can insult you to death. He has some kind of magic that lets his voice carry? Part of his job is to try and make sure people don't climb between Worlds on the tree. The rest of his job, I guess, is he wants to end the world, so even though Yggdrasil is his home he does his best to make it fall."