Rolling Shutter Effect
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, even though the whole frame is displayed at the same time during playback. This produces predictable distortions of fast moving objects or when the sensor captures rapid flashes of light.
CMOS gets this cos its a rolling shutter usually whereas CCD is usually a global shutter.