The natural reactions or cues to action which occur on what is essentially a subconscious level. Most people have a natural impulse to, for instance, jump when they hear a loud noise. This is probably as a direct result of loud noises once being associated with large animals, and the general wisdom of the time being that when large animals were about it would be best if you removed yourself. Natural impulses can be dampened by acclimatization: that is to say that the more time you spend in an unnatural world, the more tamed your impulses will become. People who live next to large factories will barely even flinch when you pull that old pop the paper bag trick. Alchohol and drugs have a similar effect upon you, to a degree that can occasionally be dangerous, as when you have only a hazy recollection of vomiting in your sleep the night before.