Will-o'-the-wisp also known as will~o~wisp or simply as wisp and willow .was thought to be a spirit or soul dwelling mostly on cemetery ground or swamps .

Now thought to be gasses emitted by decomposing biological matter and inflaming on contact with air thus generating small dancing flames or lights .

This phenomenon spawned a cartoon series called Willow the wisp , where a friendly spirit told children about fantastic tales that happened in a mysterious dark forest .