crazy little woman: No two of *anything* that size are exactly alike --
peas in a pod, 6-32 nuts out of the same box, raindrops, grains of sand. There are too many atoms in such a thing to expect an exact match, and -- even if you imagine by chance the same number of atoms -- too many ways to arrange them. If you want exact resemblance, you have to go down to the scale of molecules.