Please sit down before watching this video. It will blow your mind, and that can be dangerous while standing up.
Using inaudible sound waves, a clever chap has figured out how to make water apparently freeze — and even flow backwards.
According to Popsci:
The effect is caused by syncing up a camera with the vibrations of the water. The speaker behind the stream of water is generating a 24 hz sine wave, and the camera is filming at 24 fps, which causes the water to appear frozen.