Coal and Ash

Anytime there's a reference to ashes, charcoal, or anything else burn-y, it's a reminder of the otherworldly nature of the Everneath. This makes sense, given that the place itself is physically located in an underground-ish place. Nikki's vision of the Tunnels reinforces this:

I was in a long, dark tunnel with walls of coal, hundreds of pale hands sticking out, flailing. (3.37)

Okay, first, that's kind of creepy. Second, though, it shows that coal is part of the structure of the Everneath. When Cole—whose name, we should note, sounds like coal when you say it aloud—visits Nikki during her Return, she notices an ashy smell to him: "He blew out a breath that smelled of ash" (3.27). Coincidence? We think not.

Another coal reference appears when Cole shows up to taunt Nikki at school as "Neal." She tries to deny knowing him, but he says he's certain they've met. To prove it, he says she's "Nikki Beckett. Seventeen. Sweet. Great little tattoo on her shoulder that tastes faintly of… charcoal" (10.13). How can a tattoo taste like anything? We're not entirely sure, but Cole is signaling to Nikki that her mark from the Shade is linked to the Everneath—and reminding her she is, too.

All these references put together remind us that the Everneath is underground, and that Cole is not human. They also bring to mind references to darkness. Ever heard something describes as black as coal? It's a way of saying something's completely dark. And while darkness can be literal—it's hard to see underground, for instance—darkness can also be metaphorical. And this clues us into the fact that not just Cole, but the Everneath and everything associated with it, isn't very nice.

Plus, coal and ash are the byproduct of burning things, leading us to associate the Everneath and its denizens with living things being consumed—or, you know, all burned up.