We don’t usually think of fluids forming corners, but they can. Here you see liquid nitrogen in a simple pot. Since the pot is much hotter than the boiling point of the nitrogen, the liquid nitrogen is floating on a layer of its own vapor. This is called the Leidenfrost effect. That nearly frictionless contact with the pot means that stirring the nitrogen conveniently spins it up into these rotating polygons, visible in high-speed footage. The faster you stir the nitrogen, the more points you get.
Check out the full video below for instructions on how the researchers constructed their set-up. If you try it, though, remember to have plenty of ventilation. When the nitrogen vaporizes, its volume increases dramatically, and if you’re not careful, it will displace too much oxygen and make it hard to breathe. (Image and video credit: A. Duchesne et al., source)