Neither was born, so neither had an umbilical cord, so neither has a belly button.
A man dies and goes to heaven. There are thousands of people there, all naked and all looking as they did at 21. He looks around and almost at once spots Adam and Eve. How does he know it’s them?
Give me a hintThe hint
Adam and Eve were never born.
Reveal the answerHide the answer
They’re the only ones without belly buttons
Source: Anonymous, in Paul Sloane’s top ten lateral thinking puzzles