Spontaneous combustion is a phenomenon where materials ignite without an external flame, often due to heat buildup from microbial fermentation or auto-oxidation. The discussion highlights experiences with compost piles, where heat from decomposing organic matter can lead to smoke and even flames, as observed with sheep manure and lawn clippings. Barn fires in agricultural areas have been attributed to the spontaneous combustion of green hay bales, raising questions about the fermentation process and its ability to generate heat while still allowing some microbes to survive. The conversation also touches on spontaneous human combustion, noting that cases often involve non-mobile individuals and a nearby source of fire. The combustion of organic materials, including humans, is linked to their composition of sugars and fatty acids, which can release energy through oxidation. Overall, the thread explores the mechanisms and real-life observations of spontaneous combustion in both organic matter and potentially in humans.