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June and Jennifer Gibbons (born April 11, 1963; Jennifer died in 1993), identical twins who grew up in Britain, are a curious case involving psychology and language. The twin sisters were inseparable, and had speech impediments that made them difficult for people outside their immediate family to understand.

When they turned 14, after a succession of therapists had tried unsuccessfully to get them to communicate with others, they were sent to separate boarding schools in an attempt to break their isolation. This was a disaster: the pair became catatonic and entirely withdrawn when parted.

The girls had long had an agreement that if one died, the other must begin to speak and live a normal life. During their stay in the hospital, they began to believe that it was necessary for one twin to die, and after much discussion, Jennifer agreed to be the sacrifice. Within hours after their release in 1993, Jennifer died of sudden inflammation of the heart. There was no evidence of drugs or poison in her system. To this day, Jennifer’s death remains a mystery.