The copper earring you see here had already been glowing bright orange for half an hour when we took the photograph. There is no flame under it, no electric current through it. Underneath is a pool of volatile and highly flammable acetone, but the liquid is not on fire. So where is the heat coming from?
Last year, I stuck my hand in super-cold liquid nitrogen for the amusement of PopSci readers. My skin survived that demonstration, but I wimped out on a related experiment at the opposite extreme: dipping my finger into molten lead. That’s because the only time I’ve ever burned myself badly enough to need a doctor was while casting a lead plaque as a kid.