I have absolutely NFI.
Well, I’m not sure it begins to get to the heart of your question, but gerbils are little rodents that are kept as pets, about the size of a hamster, but with a long tail, and longer back legs (like little kangaroos.) I believe they are native to some desert area.
It’s a small rodent, often kept as a pet.
You know, kind of like a doormouse. 
Photo of a gerbil is at the top of this page:
http://www.geocities.com/amergerbsoc/Breeders.html
Hope that helps.
Or a backdoor mouse! (As Urban Legend would have it.) 
Now, now. That’s not doormouse, that’s dormouse, as in dormant. The dormouse is the champion hibernator among mammals, often spending as much as seven months out of the year sleeping off its riotous hunt for seeds.
Crossing this with the You ate WHAT? thread, the Romans considered candied dormice (yes, the plural is really “dormice”, not “dormouses”) a delicacy. I’ve seen clay plots that were essentially primitive Habitrail sets; you put a dormouse in, and fed the little sucker grain until it was to fat to squeeze out of the holes again. Then you poured in the boiling honey…
Akatsukami, consider yourself WHOOSHED!
I have the feeling that the OP was maybe referring to the rumored sexual uses of said rodent… if so, we probably haven’t helped him much… and I don’t intend to right now either, because my girlfriend is here, and may wander over at any moment to see what I am up to… if she sees me typing furiously away about stuffing gerbils up people’s assholes, I’m liable to end up with my keyboard stuffed up there as well (she thinks I have a dirty mind…)
Let’s get this straight.
A gerbil is like a small beaver … no, that’s not right … they enjoy being in confined spaces … um … they enjoy nibbling on nuts … well…
Another thing: how is it pronounced? I’ve heard both options.
So, is it gerbil with a g as in “gigantic” (the first g, of course), or with a g as in “glue”?
I have always heard it pronuonced with a g as in gigantic.
You can also shoot them out of a cannon.