When the words are separated, water and sand are exposed, which is soil ().

Less water and less sand are exposed, that is, soil (embankment)

This form of couplets is called "split character" couplets, which is a word game.

A short story:

Once upon a time, two scholars were good friends. One day, when they passed the foot of the mountain, they saw a woodcutter leaving with firewood.

A man said, "This wood comes from the mountains, please change the sentence." It's embarrassing that a certain B is not worthy at the moment.

A certain B is very unhappy. When he came home in the evening, he looked up and saw smoke billowing over the village, and suddenly realized that "the smoke at night is mostly because of fire"!

Observe life carefully, wonderful words are everywhere.