How do you know which is which? Master electrician shows you where a GFI outlet tells you the answer. [I thought my eyesight was failing when I tried to read "line" and "load" in English and French. How bad will my eyes be when they indent Spanish into the dark plastic on these?]... He also shows how the holes on the back of a GFI won't hold on to the wires the way regular receptacles' holes do.