Reporting in the journal Nature Physics, William Irvine and Dustin Kleckner, physicists at the University of Chicago, have created a knotted fluid vortex in the lab—a scientific first, they say. The knots resemble smoke rings, except these are made of water, and they’re shaped like pretzels, not donuts. Understanding knottiness has extra-large applications, like learning more about the dynamics of the sun.