Bonds between siblings isn't uncommon. But it's said that the bond between twins might be deeper or more intense than a non-twin sibling relationship.  The bond between twins June and Jennifer Gibbons was nearly supernatural - from near birth, these twins almost acted as if they were one person split into two bodies. An agreement early in their childhood to never speak to adults, their ability to mimic each other's movements even while separated, and their almost inability to live without each other soon became an inability to live WITH each other. Each girl had to find a way to co-exist while feeling "possessed" by her sister, and the only way out appeared to be unthinkable.