Four-year-old Krista and Tatiana Hogan are the only conjoined twins known to share a piece of brain tissue one of their doctors calls a "thalamic bridge." They seem to be able to feel one another drinking, to taste what the other is eating, even to see things only visible to the other twin. In many ways, they're also normal toddlers, but their case is so fascinating that it caused one psychologist to exclaim "OMG!!" This may be the first time a medical expert has been quoted using that phrase in the history of the Times.