This may look like a magic trick, but YouTube user Brusspup is just using the science of sound waves and camera frame rates to make this stream of water dance.
Brusspup ran a rubber hose past a speaker and played a 24hz tone though the speaker, vibrating the tube with a 24hz sine wave. He then filmed the stream of water pouring out of the tube with a 24 frame-per-second camera, capturing these curves. When he changes the frequency of the tone to 23hz, the water appears to be moving backward to the camera's eye. When he changes it to 25hz, it appears to be moving forwards, but in slow motion. To the naked eye, it looks like an ordinary stream of water.
If you don't have a 24fps camera, you can still see the curving water stream, but you'll need a strobe light flashing at the correct frequency.