Horse. A friend of mine brought some from Iceland and was kind enough to share. Its somewhere between pork and beef to me.
The fermented shark he brought back on the other hand, was the worst thing I have ever tasted. The smell alone cleared the room, and as one chef instructor said, “it smells like dirty pussy”.
It's a particularly gross Icelandic liquor. Some people enjoy it apparently. Wikipedia says that it has hints of the flavor of fresh rye bread. I strongly disagree.