Why can't you swallow quickly several times in a row?

Swallowing is a reflex act associated directly with irritation of the root of the tongue, subsequently contraction of the muscles that lift the soft palate and muscles of the tongue, etc. Swallowing in the absence of food or saliva in the mouth is impossible, because there is no irritation of the tongue root. It is easy to verify this by making several swallowing movements in a row: the first movement is easy, since there is always a small amount of saliva in the oral cavity; in the absence of saliva, swallowing movements fail. And the evidence of the reflex nature of swallowing are experiments in which the sensitivity of the pharyngeal mucosa is destroyed by smearing it with a solution of cocaine - while swallowing cannot be carried out. Also, swallowing is impossible after cutting the afferent nerves of the pharynx.

And by the way, when we are greedy. We drink something, don't we swallow constantly, many or several times in a row? Or I don't understand the question ... What does it mean to swallow several times?

To swallow, you need to have something to swallow, and more or less liquid: saliva in general. Swallowing something voluminous but dry, such as sand, will also not work. By the way, it doesn't have to be unappetizing sand. If you put corn sticks in your mouth, you will need to chew them first to soak them in saliva. Only then can it be swallowed. In general, this is a defensive reaction, why scratch the esophagus, we have only one, and damage to the esophagus threatens with hunger. And the stomach is adapted to digest food pre-processed by the mouth.