The word "Scud" comes from the ancient postal system. In ancient times, transportation was not as convenient as in 214, so it was not easy to separate the information between the two places.
since the Han dynasty, China has officially developed a postal service system (it existed before the Qin dynasty, but it was institutionalized in the Han dynasty, and it was issued with the postal post order), that is, the "postal post station". A post office is a bit like a modern post office plus a hotel, which allows people and mounts who deliver messages to have a place to rest. At first, the post office was used exclusively for official business (it was only after the Yuan Dynasty that it began to accept the handling of folk books and documents), usually for military purposes. When there is very urgent information to be transmitted, a courier will be sent to travel nonstop for days and nights. Even when you arrive at the post office, you will not change horses. Be sure to deliver the letter in the shortest time!
This kind of urgent military document usually has a feather stuck on the corner of the envelope, which is called "feather bang". Wang Wei's Old Generals: "war-clouds are spreading, under the Helan Range, back and forth, day and night, go feathered messages." Sometimes in places where horses can't reach, people who are good at fast running will be sent to find ways to deliver the feather book. These people are called "quick steps", "quick feet" or "fast runners"! Later, people quoted this allusion, calling those who are as fast as flying "Scud", which means that these people are strong enough to take the responsibility of sending feathers, running like sending emergency military intelligence, and the speed is very fast. (Tai Zong, a god warrior in the Water Margin, is a typical scud.)
It is said that a child was born, flying over the eaves and on the grass. Later, it was found that there was hair under the child's feet. After adults cut off the hair on his feet while sleeping, the child would not fly, just like normal people. Later, people who run fast are called Scud.