The science-for-kids show 3-2-1 Contact once had a visual depiction of how water boils that has stuck with me for years. A cartoon pot is filled with blue circles, which are supposed to represent water molecules at room temperature. A lid is placed on the pot and a flame is placed underneath it, and as time goes on, the molecules begin to move and bump into one another, increasing their temperature and the speed at which they move around. Eventually all that movement and heat results in the pot coming to a full boil, represented by the circles turning a bright red.
This image always enters my mind when I read internet discussions that catch fire and turn into vicious flame wars—the individual actors in the argument are the molecules, their words a cool blue before the bouncing up against each other increases the velocity and the temperature of the discussion, until the metaphorical lid is about to be blown off. Flames, boiling water, same difference, right?