Ratatosk is the squirrel who there shall run
On the ash-tree Yggdrasil;
From above the words of the eagle he bears,
And tells them to Nithhogg beneath.
Ratatosk is a fascinating little bastard. As the squirrel who bounces up and down Yggdrasil, he incites a war of insults between Nidhogg, who gnaws beneath, and the unnamed, but supposedly wise eagle that, perhaps, ought to know better. Similarly to most European characterizations of rodents, Ratatosk is characterized as a sniveling creature that has nothing better to do than incite trouble. Even the Norse hated gossips.
Ratatosk may also be a rat, as his name translates from Old English to mean "rat tooth". If so, that makes Ratatosk doubly vile, as the rat has a long and ugly history as not just an untrustworthy little bastard and a thief, but as bearer of fleas, and via them, the plague. Oddly, despite these associations, or, perhaps, in an oddly appropriate way, because of them, Ratatosk has been taken as a patron of communication, and may be found on everything from Asatru groups to various other pagan or geeky sites.
Given the parallels drawn between the World Tree in the modern day pagan movement, Oh My Goddess! and elsewhere, Ratatosk as a carrier of insults makes odd sort of sense. Consider him the 4chan of Yggdrasil, or perhaps IRC.