We often comment on the likeness between family members, how they have the same eyes or mouth. But by combining a half of each person, the end result can be rather unsettling, even disturbing. The viewer is confused about what they are seeing, often not able to recognise that it is two people. It is not until each half is blocked out that they are recognised as individuals.
These people were photographed at the same time then split and merged in Photoshop with a little post processing work on the join, the genetic features just fit together.