I believe one of my sisters, the one who went into the Army, over a decade ago, she told the rest of our family how soldiers in the field are supposed to heat up their MREs. There's a chemical mixture that is to mixed together that produces a strong exothermic reaction. Not exactly enough to severely burn a human, but enough to quickly heat up a MRE's contents so you're not eating up to ice cold MREs potentially out in the middle of nowhere.