Has anyone noticed that some whole objects that are singular become plural when they’ve been broken?
For example, if you take an egg, crack it into a pan and scramble it, this one egg becomes eggs! Whether it’s two eggs, twenty eggs or just one egg, after it’s scrambled, it’s called eggs. However, when a little bit of it falls on someone’s shirt, it suddenly becomes uncountable and is called just egg.
If you dissect a dead animal, you can take out its brain. Then you have a brain in your hand. However, if the same animal has been hit by a car, the brain has been crushed, and it is spread out on the street, we call it brains. Even if we know that substance comes from only one brain, we still call it brains.