The explanation of the white horse passing through the gap: the horse galloped through the narrow space at a very fast speed and was fleeting. Describe how time flies.
In addition, there are:
Time flies, the sun and the moon fly, fleeting, the stars move, the time flies, the years are like songs, the sun and the moon flow, the cold comes and the summer goes, the years fly, the water flows, and the dead are like this.