Which squirrel runs up and down Yggdrasil carrying messages?

Which squirrel runs up and down Yggdrasil carrying messages? Ratatoskr is the answer.

In Norse mythology, Ratatoskr is a squirrel that travels along Yggdrasil, the immense world tree connecting the cosmos. In the poem Grímnismál, he carries the eagle’s words from the tree’s crown down to Níðhöggr, the dragonlike serpent gnawing at a root below.

The Prose Edda gives Ratatoskr a sharper personality: rather than simply delivering messages, he carries slanderous gossip between the eagle and Níðhöggr, provoking their hostility. This makes him less a neutral messenger and more a mischievous go-between.

The other choices are creatures associated with Yggdrasil but have different roles. Veðrfölnir is the hawk perched between the eagle’s eyes, while Níðhöggr dwells beneath the tree. Hræsvelgr is a giant who takes eagle form in another part of Norse cosmology. Ratatoskr’s name is often interpreted as “drill-tooth” or “bore-tooth.”