This is a powerful code. If a listener does not understand or follow what is being communicated, communication is not taking place. Everyone has a right to indicate that he or she is not following what is being said. It may be that a particular person has a hangover or is slow-witted, but that would be an unfair assumption. If more than one person shows code 9/1 then something needs to be done. Even if it is only one person, the speaker should make an effort to repeat and simplify what has been said. There are subjects which are indeed complex. But if you are communicating such subjects you have an obligation to make them understandable to your audience. It may be very difficult but that is the speaker's problem. The speaker cannot shift the problem to the audience and tell them to be smarter. If the listeners are being asked to consider, react to or decide upon what is being said, then they have to understand what is being said. Unless the code is being abused (by someone who understands perfectly well), then the speaker should seek to take it into account. With code 9 there is no longer any need for someone to sit there in confused darkness at a presentation.