Rolling, Rolling, Rolling Shutter
Rolling shutter is a method of image acquisition in which each frame is recorded not from a snapshot of a single point in time, but rather by scanning across the frame either vertically or horizontally. In other words, not all parts of the image are recorded at exactly the same time.
— Wikipedia: Rolling Shutter
If you have an iPhone, or any other device with a rolling shutter, try out this technique yourself. More inspiration can be found in our search.