Dr Josef Mengele also known as the 'Angel Of Death' used about 3,000 twins, mostly Romany and Jewish children, for his painful genetic experiments.
Only about 200 survived.
His experiments including taking one twins eyeball and attaching it on the back of the other twin's head or changing the eye color of children by injecting dye.
In one instance, two Romany twins were sewn together in an attempt to create conjoined twins.