Moiré

Point a camera at a tightly woven shirt, a distant brick wall or a speaker grille and you can get bands of shimmer that were never in the room. It happens because the detail is finer than the sensor can resolve, so the two patterns interfere with each other. Colour fringing often turns up with it. Removing it afterwards is difficult and generally means blurring the area, so handle it at the shoot: change the guest's shirt, move the camera slightly, alter your distance, or shift focus a fraction. It is a good argument for checking a proper monitor on set, because a small camera screen hides it completely.