TSA expects/requires you to speak when you cannot do so. TSA also tells people to remove braces and casts on injured body parts and then tells those people to walk through the MMW. (Or to get up out of a wheelchair and walk like Lazarus.) Why does TSA request passengers to do something that could very well be harmful the passenger? Unfortunately, most people don't know to refuse such a request because they are intimidated by the false belief that screeners (sorry, Sai, I refuse to call them "officers") have some kind of legal authority to arrest them if they refuse.