The umbilical cord normally passes through a small opening between the muscles of the tummy (abdominal wall). If this opening does not close after birth, it becomes an umbilical hernia (trying to explain in the simplest of terms). The opening (covered by skin of the navel ) may allow intestine protrude into it when the child cries, coughs or does anything that puts pressure on the tummy. Normally this protrusion can go in and out of the opening, but the hernia may get complicated if what comes in and out gets stuck in it.