It was quite weird for Zhang Heng to see his other-self.
His second-self was still wrapped in something like a cicada pupa, with fluid surrounding it as if still growing in a mother's womb. Other than that, Zhang Heng also noticed a fist-thick fibrous tube inserted into the creature's brain. This might explain the perfectly-shaped fourth ventricle they saw on the CT image.
The other end of the fibrous tube was connected to a smaller pupa. The thing inside it was trying to break through the pupa's thin film and crawl into the tube.
At this point, Zhang Heng has basically figured out how they replaced humans.
They did not get into their target's head. Instead, they had found a way to clone a human body. This body was like a garment. Once that thing got into the brain, they could start to talk and act like a human. It was no wonder why they had been so inefficient and had not attacked him for so long.
