English speakers habitually use "skies" and "brains" when referring to singular entities. This doesn't make sense. Go outside and look up. See that? It's the sky. There's only one, yeah? It is indisputable... unless you're on some potent hallucinogens—in which case, hook a brother up. Yet we say "skies" all the time, not thinking how absurd it is. And now I'm here to darken said sky and rain on your palabra parade.
As for "brains," you surely know that humans are blessed—or cursed, as the case may be—with one per head. So when you finally come to your senses and put a loaded gun to your noggin and pull the trigger, you blow out your brain. Yet nobody says it that way. It's always "brains."
The thing is, though, if you have more than one brain, you're probably going to have trouble finding hats that fit. Beyond that heady predicament, it would be even harder to make decisions with competing cortices. Be grateful for small mercies, and do try to keep the single brain in your skull as excrement-free as possible.
While I have your attention, check out the best track from Peter Green's In the Skies.