@Mega & @SisOfNight you had an interesting discussion there

I see Mega's point but as you said written description isn't easy and don't forget that duality is an interaction and describing interactions is harder than describing type since you'll either make it abstract and harder to relate to real life or you will give a written example which doesn't capture the non-verbal clues in the interaction
So I think using pics to fill the gap is really helpful (true some will get it wrong, but it shows that they didn't understand the written description so others with better understanding can help and explain it better)
and since it is an interaction as I said, I am afraid to say that I agree with @Sol that videos are the best way to show it < but personally I won't go search for videos that shows duality