Beef Tongue or ox tongue
Often sold cured with salt and smoked. Though tongue can be tough, it is very flavorful. The Japanese and Koreans slice it very thinly and then either grill or pan fry. Many European cuisines cook it for long periods to make it more tender. It is a popular meat in tacos in Mexico.
Almost all preparations peel off the outer skin before eating. Boiling whole for an extended period makes this removal much easier.