EMBRYO ABSORBS ITS TWIN
Scientists are not sure how unborn twins in the human body originate, but the error probably takes place when the egg divides into identical twins.
A fertilized egg divides in two –a process, which normally results in identical twin embryos.
But things can go wrong. Instead of becoming two separate embryos, one absorbs the other.
The absorbed egg exists as a parasite in the other twin's body, developing into an immature, unborn twin.