This glowing, molten liquid captured by the Slow Mo Guys is thermite. The chemical reaction behind thermite is highly exothermic, hence its intense glow. There’s some great fluid dynamics hiding in this video. First, there’s the dripping thermite (Image 1), which breaks up into droplets via the Plateau-Rayleigh instability before shattering when it hits the ground.
Then there are the sequences (Images 2 and 3) of thermite dripping into water. The heat of the reacting thermite vaporizes a layer of water around it, creating a bubble that completely envelops the thermite. In other words, the falling thermite is supercavitating! That layer of air significantly reduces drag on the thermite and it insulates the thermite from the cooler temperature of the water. (Video and image credit: The Slow Mo Guys)