This is the 3008th most frequent Chinese word.
肚子
Belly; stomach.
The word "肚子" (stomach) is used to denote the physical organ where hunger is felt.
我的肚子饿了，不如去吃点东西吧。
My stomach is hungry; let's go eat something.
Here, "肚子" is used figuratively to describe the location of physical discomfort caused by laughing too much.
她不停地笑着，肚子都疼了。
She laughed so much that even her stomach hurt.
In this sentence, "肚子里" metaphorically refers to the inner self holding emotions or thoughts.