Along with onions and oatmeal, some of the dish's main ingredients include sheep's heart, liver and lungs, and the whole thing is traditionally encased in the animal's stomach and left to simmer for three hours.
This description may sound nauseating, but no less an authority than the Larousse Gastronomique encyclopedia says: "Although its description is not immediately appealing, haggis has an excellent nutty texture and delicious savory flavor." Still, good luck bringing it on a plane. Sheep's lung, an ingredient in authentic haggis, is banned in the U.S.
Like any sausage or hotdog as long as you don't know what's in it it tastes just fine.
Shame we can't get the "real thing" here.