The doctor that Sofia is talking about as she recounts her time in Auschwitz is the infamous Dr. Josef Mengele. He was notorious for selecting those that came off the cattle carts for those who lived or were sent to the gas chambers. He was particularly interested in experimenting with people, whether it be freezing people in sub-zero water or changing the color of the iris of eyes. He also had a deep interest in twins and would do organ switching, blood transfusions or sewing twins together.
When Rabbi Sendak opens the Hebrew book in his office, he thumbs through it in the wrong direction. Hebrew is written in the opposite direction to English; a real rabbi would have opened the book and read it from right to left.