Josef Mengele would inject chemicals into the eyes of children in hopes that it would change their eye color.

Mengele would do experiments by doing surgeries without anesthesia, transfer blood from one twin to another, isolate children, injections, and removal or addition organs and limbs.

Mengele thought he could make Siamese Twins by connecting blood vessels and organs together. The Gypsy twins he used screamed in pain for three days, and died from gangrene.

Josef had a interest in twins because there wasn't much information on twins. Since Josef had a huge amount of power he requested his assistants to look for Jews who were twins. This is how he was able to experiment on them.