They boil the entire head of the pig! *barf*
From Wikipedia:
Scrapple is typically made of hog offal, such as the head, heart, liver, and other scraps, which are boiled with any bones attached (often the entire head), to make a broth. Once cooked, bones and fat are discarded, the meat is reserved, and (dry) cornmeal is boiled in the broth to make a mush. The meat, finely minced, is returned, and seasonings, typically sage, thyme, savory, and others are added. The mush is cast into loaves and allowed to cool thoroughly until gelled. The proportions and seasoning are very much a matter of the region and the cook's taste.
Commercial scrapple often contains these traditional ingredients, with a distinctive flavor to each brand. A few manufacturers have introduced beef and turkey varieties and color the loaf to retain the traditional coloration derived from the original pork liver base.
Vegetarian scrapple, made from soy protein or wheat gluten, is offered in some places. It is seasoned to be much sweeter than typical meat scrapple.