The eastern North Carolina whole hog sandwich is defined by a refusal to choose a cut. Where a pulled pork sandwich is shoulder and only shoulder, this one is the entire animal cooked at once and then chopped together, so the dark, fatty meat from the shoulder and belly is blended with the lean, mild meat from the hams and bits of crisp skin into a single seasoned mixture. The flavor of the sandwich is that blend, and it is a flavor no single muscle can produce. The whole point is that nothing is set aside: the balance comes from the proportions of the whole pig, not from a butcher's selection.
The craft is the longest in American barbecue and the least forgiving. The split hog is cooked low over wood coals for the better part of a day, the heat managed by hand so the lean hams finish moist at the same moment the fatty shoulders render and the skin crisps. When it comes off, the whole animal is chopped together on the board, and the only seasoning is a thin vinegar-and-pepper sauce worked through it as it is chopped. That sauce is doing structural work: the acid cuts the richness of the blended fat, and its thinness lets it penetrate the chop rather than coat it, which is why an eastern hog is dressed and not glazed. The bun is plain and soft and meant to disappear, and a scoop of crisp, sharp slaw rides on top to supply the cold crunch and bright acid the warm mixed meat has none of on its own. It is assembled fast and eaten without ceremony, the way food cooked for that long is meant to be.
The variations sit along the same regional line and are codified rather than loose. The Piedmont version around Lexington steps back from the whole hog to shoulder alone and tightens the vinegar with a little tomato into a red dip; the pulled pork sandwich is that shoulder build generalized; the slaw dog runs the same eastern flavors over a frankfurter instead of a bun. Each of those deserves its own article rather than being crowded in here.