If you play around with an ultrasound field for long enough, you can set up standing waves that allow you to levitate water drops in mid-air—but that's only where the fun starts.

The drops, held in a node of low pressure and supported in mid-air by a high-pressure zone sat beneath them, can be excited by different frequencies of ultrasound. When the frequency matches a multiple of their resonant frequency, they show weird modes of oscillation, forming stars with three, four, five or however many points—the number matching the multiple of frequency. But all that science aside, don't they look pretty? [New Scientist]

(Oh, and excuse the music. Please, please, please, excuse the music.)