Berk. The name doesn't sound familiar, and given that Castiel's seen the whole of Earth over the course of his long life, that most likely means that Toothless is in fact from a different world.

Berk may be the name of the area you live in, but the entire world should have its own name. It's interesting to realize that a dragon would have such a small scope of things, when he has wings that can carry him from land to land.

Castiel's familiar enough with viking death rituals to know what Toothless is referring to, and he nods. That's a way to put a human to rest, but after that their soul leaves their body and ascends to Heaven. Or Valhalla, as vikings would call it. A different name, but the same concept.