Sometimes, people need popcorn. Like, immediately. Sometimes their need for popcorn is so strong that they just can't wait the minutes that it takes to pop popcorn on a stove or in a microwave. That's why we can all be thankful for this dude and his explosive instant popcorn steam cannon.
There's some preparation that goes into preparing the machine for firing, but it's definitely worth it to stick through the first 30 seconds of the video for the payoff. And as far as what's actually happening, the consensus seems to be that popcorn kernels are placed inside a pressure cooker along with oil and water. The cooker is kept turning to keep the kernels from burning, and the pressure inside is high enough that the kernels are unable to pop. When the lid is released, the water flashes into steam, the pressure drops, and the kernels all pop at once: