From Global Gourmet.com...
But what parts of the hog go into the creation of scrapple? After the ham, bacon, chops and other cuts of meat are taken from the butchered pig, what remains are fixings for scrapple, including the meat scraped off the head. Scrapple may contain skin, heart, liver, tongue—even pork brains. Those faint of palate needn't venture any further.
Note: also may contain pig eyeballs. They don't waste anything when they make scrapple!