I like the steam plumes from the battery vents that accompany a thermal runaway. You can almost hear the airplane cry to you "Call the fire department and order some servicable batteries". Some unimaginative types have gotten the batteries out of the plane under these conditions, but I'd hold out for some good protective gear first before I tackled the problem.. .. .As Blacksheep implied, the battery turns into a molten mess inside its metal case. Makes a good audio/visual training aid, after it cools down.