This happens more frequently than you thought.
Even right now, if you try to swallow saliva multiple times as fast as you can, consecutively; you will hit a "bottleneck" :)
Oesophagus, operates on a rhythm, of which is initiated by the back of your tongue (where tonsils hit)
But, oesophagus, having mind of its own (involuntary); does not accept initiated rhythm, if it's "out of timing"
This "timing" is dictated by the way muscle contract and relax as they push saliva you just swallowed down into your tummy. Nasty yet brilliant ain't it?