This impressive video begs the question – what is an ultrasonic vortex beam, and why is it so clever at manipulating objects? Briefly, an ultrasonic vortex beam is rather like a laser beam with an axial phase singularity. This means that the phase of the sound wave varies as you orbit a given spot on the optical axis. As the orbit is drawn smaller and smaller, the same amount of phase change is found. As a result, on the axis of the beam it has all possible phases at once. As this is not allowed by conservation and continuity laws, the on-axis ultrasonic intensity has to be zero. The cross-section of an ultrasonic vortex beam thus appears a bit like a donut – no signal on axis (the donut hole), a large signal away from the axis (the thick part of the donut), and a signal that falls off as you look further from the axis (you run out of donut).