What do we learn about the man through his exchanges with the Road Rat?

Key elements in the man's characterisation arise in his exchange with the Road Rat as acquired traits and knowledge is alluded to in particular as the man describes why the Road Rat will not hear the gun shot. Not only are we shown the man's ability to think quickly in a difficult situation but it is revealed that the man possibly has and interesting history in medicine as the man says 'Because the bullet travels faster than sound. It will be in your brain before you can hear it. To hear it you will need a frontal lobe and things with names like colliculus and temporal gyrus and you wont have them anymore.' or defense/combat in 'The man had already dropped to the ground and he swung with him and leveled the pistol and fired from a two-handed position balanced on both knees at a distance of six feet.'. By using jargon and complex lexis like 'colliculus' and 'temporal gyrus' it is impossible that the man hasn't had some kind of medical training or education which would teach him these complicated terms and how to use them and by combining this knowledge with his obviously deft skill in combat gives reason to deduce that the man had a particular profession which involved all of this skill set. Whatever that may have been we know that it gave him the skill to survive which is presented here and at other parts of the novel (such as the scene when the explosions hit with his wife when he immediately filled the bath).