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Watch water freeze and flow backwards in elegant optical illusion

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With the right camera, a speaker, and a rubber hose, you can make water appear to freeze, move in slow motion, or run backwards. The below YouTube video by user brusspup demonstrates a fascinating optical illusion that — according to him, at least — isn't difficult to replicate with the right equipment. The key is to use a camera that shoots at 24fps, then run water past a subwoofer placed close enough to vibrate the hose, making the vibration of the water match or nearly match the recording speed of the camera. The result is that the water is caught at almost the same point in its vibration each frame: at 24 Hz, it looks to be standing still, at 23 Hz it seems to run backwards, and at 25 Hz brusspup says it moves in slow motion. It's only, of course, visible through the camera, not with the naked eye. Brusspup posted a preliminary version of the experiment last year, but it's now better shot and even more impressive.