An open mouth, smiling slightly — one of the simplest drawings on the oracle bones, and one of the busiest characters ever since. A mouth speaks (说), sings (唱), asks (问), and eats (吃); wherever 口 appears inside a character, something is being said or swallowed.
A piece of culture
Counting mouths The Chinese word for population is 人口 — literally "person-mouths", because for two thousand years the empire counted its people by the mouths it had to feed. The Han dynasty census of the year 2 CE registered about 60 million people, one of the oldest surviving censuses on earth. Emperors rose and fell by that number: more mouths meant more farmers, more taxes, more soldiers — and more to lose when the rains failed.
Use it in a real word
人口
rénkǒu · jan4 hau2
population — literally "person-mouths", and you already know 人