Naturally, the Art of Perfect Cloning was much more precise than anything modern technology could offer.
There were virtually no differences between the clone and the actual being.
Shen Xing and Fei Xue stumbled upon two perfect bodies when they were searching for divine herbs back then, and after dissolving and harnessing them for many years, the bodies could contain their Saintly souls.
After that, they transmuted their Nascent Gods into the bodies.
Lastly, with their almighty powers, they severed any connection the bodies had to themselves and let the bodies enter a deep sleep.
They even laid down a seal on this place, which could only have been activated by the death of themselves.
Only then would some their memories be transmuted from their original bodies to the clones.
Once they woke up, they had a rough idea of what had happened.
This was the product of their years of labour.