At some point after you give birth, you will look inside your bellybutton and see enough filth to build a terrarium. It will look like a garden gnome sneaked into bed while you were sleeping and dumped in a few tons of topsoil. You will be horrified, you will think, “But I shower!!” and depending on your relationship, you will either show your partner (who does NOT want to see it) or scuttle off to clean it out with a Q-Tip before anyone else could ever know.
Don’t panic. It’s your linea negra sloughing off. If you don’t know what a linea negra is, Google it. I’m not a doctor.