Foxfire

The foxfire,—as the country people call it,—glowed hideously from the cold and matted bosom of the marsh; and, far from us, in the depths of darkness, the screech-owl sat upon his perch, brooding over the slimy pool, and whooping out a dismal curfew, that fell upon the ear like the cries of a tortured ghost.

Source: wiktionary

Perhaps you've seen a foxfire in the woods. Well, in the dark, it looks like a live, burning coal; but when you go to it, and take it up, it's only a piece of rotten wood.

Source: wiktionary

[Nathaniel] Hawthorne in one of his books records a remarkable personal encounter with this weird fox-fire, and one which cost him dearly. He was on a journey by canal-boat, which had stopped en route for a brief period at midnight. During the interval he had stepped ashore, and was decoyed into a neighboring wood by the bright glow, which proved to be a fallen tree ablaze with phosphorescence. In his surprise and interest he lost all account of time, and thus missed his boat, [...] Almost any damp woods, especially after a rain, is likely to disclose its fox-fire, but it occasionally appears under circumstances where we little expect it.

Source: wiktionary

People calls this "spunk," but it's foxfire. You see this hole in it? You see where I sawed it in two with the chain saw? See, this grows in hollow trees in a maple or a oak. No, it ain't mushroom; it's just really foxfire.

Source: wiktionary