Caporegime
A sandwich is a countable entity. It's not like, say, a pile or a hole. If you have a pile of sand and you take half of it away, there is still a pile of sand, as there is no set definition on what constitutes a "pile". Likewise, digging one hole and then digging an equivalent hole at the bottom of it doesn't make two holes, one atop the other, it makes a single hole of twice the depth.
A sandwich, however, is commonly defined as two slices of bread with some filling between them. Cutting a sandwich in half them makes two half sandwiches, as each one is clearly composed of one slice of bread and some filling.
A sandwich, however, is commonly defined as two slices of bread with some filling between them. Cutting a sandwich in half them makes two half sandwiches, as each one is clearly composed of one slice of bread and some filling.