system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do pregnant bellies "pop out" the belly button while fat bellies result in a cavernous belly button?
gpt
The back of your belly button is attached to the internal "wall" of your belly. Your belly fat grows outside that wall and surrounds your navel. A baby grows behind that wall and pushes against the navel from the inside.