Some people have anxiety disorders that mean they are unable to speak around some people, but they can speak around certain people. Opinion is divided between if this is caused by a physical characteristic of the brain, or if these people are simply socially retarded. ‘selective mutism’ to the politically correct, is not the same as stage fright, or ‘choking’ if you are an MC. Selective mutes could have a problem with talking in front of big groups, on the radio or most, in front of someone they want to nail, or someone who is about to kick the shit out of them. It's also not the same as stammering, as at-least the mutants can keep their mouths shut and generally not bother us that much with their inability to communicate.