have read. you know that nervous feeling in your stomach before an exam or a big game, the so-called butterflies that you get before asking someone out on a date or handing over your hard-earned cash for a new car? it’s as if your stomach is feeling your agitated state of mind. well, in a sense it is. the reason you are feeling those sensations is because of the entropic nervous system (ens) embedded in the wall of your gut. it consists of approximately 500 million neurons – about as many as in the brain of a cat – and is around nine meters long when unravelled. the ens has been dubbed the "second brain" and is connected to the brain in your skull by the vagus nerve.