Minced sheep's liver, lungs, and heart (the "pluck"), mixed with oatmeal, suet, and spices, sewn into the sheep's stomach bag and boiled. I grew up in Edinburgh with the stuff and I hate it, but many consider it a delicacy. Traditionally served with boiled mashed potatoes ("tatties") and turnip ("neeps") and on special occasions like Burn's Night with a glass of whisky. Search for "Macsween" on the web -- theirs are widely rated the best.