Swamp-gas, commonly referred to as marsh gas or biogas, is a mixture of gases released naturally from decomposing organic matter in wetlands or marshes. This gas is primarily composed of methane, carbon dioxide, and nitrogen, and is known for its distinct sulfurous odor. Other terms that may be used interchangeably with swamp-gas include bog gas, septic gas, and methane hydrate. These gases can be dangerous in large concentrations, as they are flammable and can also cause asphyxiation. Swamp-gas is also known for its eerie and ghostly appearance, commonly seen as wispy blue flames flickering above wetlands in the dark.