Motion blur

Each frame records everything that happens while the shutter is open, so anything moving during that window is captured as a streak. The convention is the 180-degree shutter rule: shutter speed at roughly double the frame rate, so 1/50 second at 25fps or 1/48 at 24fps. That gives the amount of blur audiences read as normal. Faster shutters freeze each frame and make pans and walking shots stutter, which action sequences sometimes use deliberately. Slower shutters smear. Shooting outdoors usually means an ND filter, since holding 1/50 in bright sun otherwise forces you to stop the lens down or drop ISO past where the sensor will go.