Conjoined twins have long been the subject of great curiosity due in part to the rarity of the condition. Not to mention, many different ways exist for siblings to become anatomically connected to one another. Fueled by that curiosity, a Soviet physiologist named Pyotr Anokhin - who studied the development and structure of human circulatory and nervous systems - made Masha and Dasha Krivoshlyapova the focus of many of his science experiments - experiments that were conducted for the majority of their lives.
These USSR-approved experiments on conjoined twins subjected the sisters to torture, isolation, and a life greatly lacking in typical human interactions. Adding to the complexity of Masha and Dasha Krivoshlyapova's situation, the sisters had diametrically clashing personalities - one showing the traits of a psychopath and the other an empath.