Other Triquetra
Twin Telepathy

This sort of psychological connection isn't necessarily mysterious, of course: any two people who know each other very well and who have shared many common experiences — including non-twin siblings, old married couples, and even best friends — may complete each other's sentences and have a pretty good idea about what the other person is thinking.

The idea of twin telepathy has been around for well over a century. It appears, for example, in the 1844 Alexandre Dumas novella "The Corsican Brothers." It tells the story of two once-conjoined brothers who were separated at birth yet even as adults continue to share not only thoughts but also physical sensations. As one twin describes, "However far apart we are now we still have one and the same body, so that whatever impression, physical or mental, one of us perceives has its after-effects on the other."