I read a story once where a young man was left to the tender mercies of a weasel like carnivore that could eat a hole in a cow from udders to throat in less than 6 seconds and moved like a track star on speed, on the good side it became slower the more it consumed and he drowned it before it could finish his pelvic region off, got stuck on the bone as i recall. so not much in the Armour piercing category, but much to be said for it's speed, initiative and damage (or number of attacks) capabilities. Also only appeared in small family units, territorial i guess.
anyway that is what comes to mind when i think of a death weasel or a giant shrew on p.c.p.(i see either as small).
P.S. if this story sounds familiar to anyone drop me a line with the title so i can read the book again, thanks.