Hey kids! Go rest your hands on a speaker playing loud music. Feel the sound vibrations? Good. Now you might want to adjust your volume for this one.
Sound frequencies produce a variety of increasingly intricate resonance patterns. And if you sprinkle sand or salt on a metal plate that is vibrating from these sound frequencies, you can see the patterns.
Did I explain that correctly? If not, Science Friday has a great video that explains it super clearly. Highly recommended.