Liquid metal is an awesome thing to play with. Mercury, the most common kind, is sort of toxic and will eventually drive you insane, but before that happens, you can make it do some amazing stuff: play music, and it dances.
Sound is a type of energy that expresses itself with vibrating molecules. Sound that we hear generally involves vibrating molecules of air, but sound energy can cause just about anything to vibrate, including liquid metals such as mercury. You can't usually see what sound looks like in air, but you definitely can in mercury, where sound waves express themselves as areas of low and high displacement that causes the mercury to deform into bizarre shapes that change depending on the frequency of the sound.
Here's what this looks like at normal speed:
And here's what it looks like slowed way, way down:
Mercury isn't the only material that reacts to sound in weird ways. By mixing cornstarch with water, you can use low-frequency audio tones to create a bizarre monster-thing that seems to have a mind of its own. You can do this at home (I've done it before), but it works out much better when a real scientist does it in a lab: