If you try to eat and talk at the same time, the epiglottis doesn't get warning of the coming of a swallow of food in time to cover the opening of the windpipe, and the food goes down the wrong way and you cough and choke.
Now, if you will just place your fingers upon the front of your neck and slide them up and down, you will, at once, feel your windpipe--a hard, rounded tube with ridges running across it,--while, no matter how carefully you feel, or how deeply you press, you cannot feel your gullet or esophagus at all.

Just take a mouthful of water, however, put your fingers deeply on each side of the windpipe, and swallow, and you will feel something shoot down the esophagus, between your fingers, toward the stomach.
Both of these tubes were made of exactly the same materials to begin with.

Why have they become so different?
A moment's thought will tell you.

One, the gullet, has only to swallow solid food or drink, so that its walls can remain soft, and indeed fall together, except when it is actually swallowing.

The other tube, the air-pipe or windpipe, has to carry air, which neither will fall of its own weight, nor can readily be gulped down or belched up.