The three most common "oops" hits that I've seen (but not necessarily made) result in short, quick recoveries...

Femural artery. Think "femur", or thigh bone. There's actually two of them. One in each hind leg. If one gets hit it'll leak like a cut garden hose.

Aortal artery (sp?). The artery that comes off the top of the heart, runs along the underside of the spine, then branches out to the two femural arteries. Pretty much the same effect as the femurals.

Spine. Needs no further explanation. Often requires a finishing shot, but no tracking's involved.

JRW