The eyes and nose

When you see appetizing food, you experience a conditioned response In other words, your thoughts — “Wow! That looks good!” — stimulate your brain to tell your digestive organs to get ready for action. What happens in your nose is purely physical. The tantalizing aroma of good food is transmitted by molecules that fly from the surface of the food to settle on the membrane lining of your nostrils; these molecules stimulate the receptor cells on the olfactory nerve fibers that stretch from your nose back to your brain. When the receptor cells communicate with your brain — “Listen up, there’s good stuff here!” — your brain sends encouraging messages to your mouth and digestive tract.

In both cases — eyes and nose — the results are the same: “Start the saliva flowing,” they say. “Warm up the stomach glands. Alert the small intestine.” In other words, the sight and scent of food has made your mouth water and your stomach contract in anticipatory hunger pangs.
But wait! Suppose you hate what you see or smell? For some people, even the thought of liver is enough to make them want to barf — or simply leave the room. At that point, your body takes up arms to protect you: You experience a rejection reaction — a reaction similar to that exhibited by babies given something that tastes bitter or sour. Your mouth purses and your nose wrinkles as if to keep the food (and its odor) as far away as possible. Your throat tightens, and your stomach turns — muscles contracting not in anticipatory pangs but in movements preparatory for vomiting up the unwanted food. Not a pleasant moment.
But assume you like what’s on your plate. Go ahead. Take a bite.