When I was a child, an old man made popcorn at the bottom of the building, brought a bowl of rice and two yuan, and then got a stove-shaped thing called a pot. Then he put the rice in the pot and roasted it with fire. When the pressure gauge reached a certain level, the rice inside exploded. The last step is to tighten the lid with a tape, and then open the lid. Only when it collapses, the glistening rice becomes a pile of popcorn and collapses into the bag.
"Bangguo" is a Tianjin dialect, which means having sex. It is used in parts of Beijing, Tianjin and Tangshan. Originally refers to the old-fashioned machine for making popcorn, which folds popcorn into many bags. Later, someone extended this, so it means clapping for love.