Some rotting wood glows faintly green in the dark, all on its own

Certain fungi that decay wood, such as Armillaria and Panellus species, produce a chemical reaction that emits a faint greenish glow known as foxfire. Sailors, soldiers and Aristotle himself noted the eerie light for centuries before biologists confirmed it comes from the same luciferin-luciferase chemistry that lights up fireflies.

— Wikipedia contributors, Foxfire (bioluminescence) — Fungal bioluminescence