In the classic NES game Castlevania II, this is what Simon Belmont would say when darkness fell over Transylvania. Simon had defeated the evil Count Dracula, but he was still prosessed by the Count's curse. And when night came, the monsters became stronger, and invaded the towns, thirsty for blood.
This is a wonderful thing to say when you realize it's not daytime anymore, or to mutter to yourself as you walk past strangers at night.