There are some small (gumdrop size) grey 'things' that reside in the fatty areas of the leg joints. That is, as you separate the shoulder or hindquarter, you'll find them in the crease between leg and body. I assume they're glands, I've found them on every hog I've processed, and they're symmetrical — that is, they appear on each side of the hog so I conclude they're not a parasite or other external item.
I look for them, and just trim them out with the soft fat that's also there. If you're looking for them they're pretty easy to find.
As redchevy says: depending upon how much fat the hog has, you may need to add some. My Wild Game Cookbook says you need at least 20% fat, 25% is preferred. That makes my wife crazy,
so I quit telling her how much fat is in the sausage.