How Hot Dogs Are Made And What's Actually Inside

After the steaks, chops, breasts, ribs, thighs, hams, tenderloins and briskets are removed, there's a fair amount of gristle, fat and offal remaining on a butchered animal, and early on, people realized this could be put to good use. One of these products is the hot dog, a classic of pre-cooked, processed meat.
A hot dog is a cooked sausage, traditionally grilled or steamed and served in a sliced bun as a sandwich. But what's actually inside a hot dog?