Riddle

"Tabatha and Samantha were born identical twins, but they go beyond that. They are somehow connected. They look exactly the same with no distinguishing features to tell them apart. If they are separated doctors have determined that they would die. These twins are always together and feel the same emotions, they have the same senses, and can even see through the other twins eyes. If these twins look identical, and share the same personalities and feel the same then how are they different?"