The rat is called LUC_PickAxeHolderHack.

Enlarged Version

Hihi ... I don't know, but if one of your two Source Hunters is a Witch (Talent: Pet Pal)
OR you can learn or buy this talent (a skillbook ?) ...
THEN you can talk to animals, so maybe can "LUC_PickAxeHolderHack" tell you who he/she is

Good luck

Nah, there is no way down there to get close enough to talk to it.

Sorry, I didn't know ...

maybe you can teleport it out of the hole or is it too far?

Too far. I was just wondering if was left there by mistake by Larian team during development and was curious as to what purpose it served them. I also just found Spider Pig in knights tomb but I think that one was there on purpose as simpsons joke maybe.

Check out some of the names of the elementals you can conjure. They are amusing to say the least.

U can Talk to it. it seems out of reach, but if you click on it to talk, your hero will start traveling to the right location where he can talk, which is on the left side of the chasm, top of it, where there are 3 crates and 2 barrels. Using your screen capture as reference , you have just to scroll a little to the left to see the higher place im talking about.
Its usefull to use B to set a top point of view, so u can click it.
i first used jahal to talk to it, and the rooster said " its uncomprensible , maybe a source hunter can help?" (or something like this)

So i get there with my Hero with PETPAL aaaand: instead of the right avatar of a chicken, like it was with Jahal, It had a question mark icon ( ? ) and no dialogue , only - 1. I'll take my leave - as answer.

Very funny!! I saw a bouncing sheep named "Party Animal" in the homestead once but it disappeared into an inactive portal before I could catch it to talk to it...that was hilarious and somewhat disappointing that I couldn't catch it. Anyone managed to talk to it?

Buggy development leftovers.

A sheep?^^ we have actually seen a pig when first arriving in the homestead... but could not manage to talk to it either...

Yep, the Party Animal was a sheep in my game, I've seen on the Steam forums some were saying it was a dog in their game so i'm guessing this character is randomly generated. But the whole scene was hysterical, pure comedy....I wish I could see it again without playing another 8-10 hours or something it took me to see it at first.

Anybody figure out how to talk to the spider pig? ^^

Wut? That's a thing in Original Sin? You sure you aren't thinking of Family Guy?

SPIDER-PIG

http://abload.de/img/2014-07-23_00001eiuy5.jpg

^^

Pretty sure the party animals appear randomly. I've had all of the mentioned ones (sheep, dog, chicken) already pass by, and indeed they cannot be talked to.
They all go to the 'Hidden Zone' portal... 0_o