A man died and went to Heaven. There were thousands of other people there. They were all naked and all looked as they did at the age of 21. He looked around to see if there was anyone he recognised. He saw a couple and he knew immediately that they were Adam and Eve.
How did he know?
The man knew that Adam and Eve were not born of women, and so neither of them did have any navel.
The absence of navel in each of the two persons led him to deduce the identity of the couple.