There's a super secret method hidden in the bowls of an old FSnH thread, which involved quite possibly the most disgusting of all animated avatars.
It's not really officially supported by all browsers if memory serves, but it is possible to do for people other than Nate.
e: It's just animated gifs that aren't allowed. I'm fairly sure the filter can tell if there's more than 1 frame or not.
Also this is the thread and the method was deleted by Nate. Worth a read, even if it will just make us all miss T-Nex more
