A. Castiel's sandwich didn't actually taste like atoms.
The angelic trueform is much more attuned to the multicomponent, complex systems that form the world, in all its structured, recursive non-Euclidean geometries. An angel's perspective is inherently aterrestrial, their sense of scale entirely apart from a human being's. But as such that feeling is beyond the scope of human cognition, except in very few enlightened cases, and Castiel acknowledges that. What he's learned on Earth, what he's learned from the Winchesters, what he learned as a human himself, is that when humans move to understand the universe, they break it down into individuated components. They attempt to find its smallest parts and know it piecemeal because this exercise obtains that sense of the defamiliar, the unheimlich, and offers the impression of extra-human perception, of a world beyond their own. It's this feeling Castiel means to convey, so he translates. This sandwich tastes like atoms, he says. And Sam nods, like he understands--or maybe like he's bored, or distracted. Still, the message is transmissible.B. Castiel's sandwich did taste like atoms.
This is what it means for a human to speak to an angel.
But having been on the other side of that division, Castiel thinks, maybe that's not it at all. Maybe this is how a human speaks to anything. How an angel learns to speak. Fits of translation--that's what it means to speak.
Angels are a raw kind of power, and to God's eye, when Creation was new, they were limitless. Consistently upgradable. They were so much power that could be bound up in so little grace, great expanses of data and self-replicating intelligence, with their own language that evolved and their own timelines that rolled and forth and effortlessly evaded paradox. But unlike earth, unlike humans, they are primordial. They are supernatural not in the sense that they are greater than, but merely prior to. Blueprints, if you will, for structural intelligence, for the invention of fluid dynamics, the mirror neurons and built empathy that would define life on Earth. They are piecemeal. From an earlier school of thought, God's thoughts, which he'd lend to his humans millenia later, to start them off, to start them off and one day, he hopes, usurp him. He wants to build a human that can outwit God, the same way humans will build computers to defeat their most calculating grand masters. Angels are not brains, they are machines. They are information systems. They are binary code. (This is what Naomi remembered. And this is why Naomi, she had to go.)
Castiel's sandwich tastes like atoms. Which is unpleasant--but more than that, not preferable. But not preferable to what, and why? Castiel is an angel again, and he does not remember.
But he thinks about Sam, Sam with Gadreel inside him, Gadreel taking up spaces and agencies that could have been Sam's, and in that moment, Castiel discovers empathy. There is a ghost in his machine. And Castiel thinks,
I am so sorry.